Added COLOR() macro to NEDsim for ease of reading.

[screensavers] / hacks / NEDsim / NEDsim.c

/* (c) 2021 Aaron Taylor <ataylor at subgeniuskitty dot com>                  */
/* See LICENSE.txt file for copyright and license details.                    */

#include "screenhack.h"
#include "simulator.h"

/* -------------------------------------------------------------------------- */
/* Front Panel Layout                                                         */
/* -------------------------------------------------------------------------- */

// All of these values are in units of 'cells', not 'pixels'. Where applicable,
// coordinates refer to the upper-left corner of a cell. See the files
// `layout_reference.*` for details.

#define OVERALL_WIDTH_IN_CELLS      70
#define HEADER_HEIGHT_IN_CELLS      14
#define FOOTER_HEIGHT_IN_CELLS      2

#define LOGO_X_OFFSET               2
#define LOGO_Y_OFFSET               2
#define LOGO_WIDTH                  20
#define LOGO_NAME_HEIGHT            6
#define LOGO_WEBSITE_HEIGHT         2

#define HALT_X_OFFSET               26
#define HALT_Y_OFFSET               2
#define HALT_WIDTH                  6
#define HALT_LIGHT_HEIGHT           6
#define HALT_LABEL_HEIGHT           2

#define WORDLINE_BITS_PER_STRIPE    4
#define WORDLINE_WIDTH              32
#define WORDLINE_HEIGHT             1

#define PC_X_OFFSET                 36
#define PC_Y_OFFSET                 7
#define PC_WIDTH                    32
#define PC_LABEL_HEIGHT             2
#define PC_LIGHT_HEIGHT             1

#define SC_X_OFFSET                 42
#define SC_Y_OFFSET                 2
#define SC_WIDTH                    5
#define SC_LABEL_HEIGHT             2
#define SC_LIGHT_HEIGHT             1

#define PSW_N_X_OFFSET              51
#define PSW_Z_X_OFFSET              58
#define PSW_Y_OFFSET                2
#define PSW_LABEL_WIDTH             3
#define PSW_LABEL_HEIGHT            2
#define PSW_LIGHT_WIDTH             1
#define PSW_LIGHT_HEIGHT            1

#define STACK_X_OFFSET              2
#define STACK_Y_OFFSET              12
#define STACK_WIDTH                 32
#define STACK_LABEL_HEIGHT          2
#define STACK_LIGHT_HEIGHT          1

#define HEAP_X_OFFSET               36
#define HEAP_Y_OFFSET               12
#define HEAP_WIDTH                  32
#define HEAP_LABEL_HEIGHT           2
#define HEAP_LIGHT_HEIGHT           1

/* -------------------------------------------------------------------------- */
/* Data Structures                                                            */
/* -------------------------------------------------------------------------- */

struct NEDsim {
   // Various X resources
   Display * dpy;
   Window    win;
   GC        gc;

   // Tracks the width and height (in pixels) of 'win' on 'dpy'.
   int dpy_width, dpy_height;

   // To ensure the NED display is always synchronized/valid, we
   // double-buffer. This is that buffer.
   Pixmap panel;

   // The front panel is defined in a fixed grid of 'cells' which are then
   // scaled and projected onto the actual screen. This variable tracks the
   // size of one 'cell' in screen pixels.
   int cell_size;
   // Like above, this variable tracks the scaled size (in pixels) of cell
   // borders when projecting them on the screen.
   int border_size;

   // Since the panel will be smaller than the display window, these two
   // variable track the location (in pixels) of the upper left corner of the
   // NED panel (pretending it didn't have rounded corners) relative to the
   // display window's origin.
   int origin_x_offset, origin_y_offset;

   // Delay (in microseconds) between clock cycles in the NED CPU.
   size_t delay;

   // Since the heap and stack areas are resized to fit the display, this
   // variable tracks their height.
   int num_data_rows;

   // This is an index into the color_list[] array, selecting a color scheme.
   size_t color_index;

   // If the display is unsuitable (e.g. too small), this boolean is 'true'.
   // With this, we blank the display but keep the simulation itself running,
   // allowing the ongoing simulation to display when the situation is
   // corrected, and allowing us to avoid boring the user with unnecessary
   // simulation restarts.
   Bool suitable_display;

   // The font size is dynamically adjusted based on display size. This
   // variable stores the full font description, including the correct font
   // size, all in the X11 font specifier format. For example,
   //             -*-helvetica-*-r-*-*-72-*-*-*-*-*-*-*
   // if the display were using a 72 point helvetica font without emphasis.
   char * current_font;

   // This struct contains all machine state for the simulated NED computer.
   struct NEDstate * nedstate;
};

struct color_rgb {
   // The type 'unsigned short' comes from the XColor struct definition.
   // The red, green, and blue values are always in the range 0 to 65535
   // inclusive, independent of the number of bits actually used in the
   // display hardware. The server scales these values to the range used
   // by the hardware. Black is represented by (0,0,0), and white is
   // represented by (65535,65535,65535).
   unsigned short red, green, blue;
};

struct color_scheme {
   // The following entries define a full color scheme for a NED panel.
   struct color_rgb
       panel_bg,  // Empty screen space not taken up by the panel
       panel_fg,  // Panel body/faceplate
       light_on,  // Illuminated data indicator
       light_off, // Non-illuminated data indicator
       error_on,  // Illuminated error indicator
       error_off, // Non-illuminated error indicator
       primary,   // Primary panel color (see: logo background)
       secondary, // Secondary panel color (see: "HALT" text background)
       tertiary,  // Tertiary panel color (see: "subgeniuskitty.com" text background)
       border,    // Cell borders
       text;      // Panel text
};

// All included color schemes for NEDsim are defined in this array. To select a
// particular color scheme at runtime, use the `-color N` CLI option.
static struct color_scheme color_list[] = {
   { // This color scheme is inspired by the KI10 version of the PDP-10.
     // Many RGB values came from: http://www.chdickman.com/pdp8/DECcolors/
       {63479,63479,63479}, // 092-XXXX-123
       { 5140, 2056, 5654}, // 092-XXXX-152
       {65535,11051,15677}, // homemade, derived from 092-XXXX-139
       {20000,13107,12850}, // homemade, derived from 092-XXXX-154
       {65535,13107,12850}, // homemade, derived from 092-XXXX-154
       {20000,13107,12850}, // homemade, derived from 092-XXXX-154
       { 4112,12850,20046}, // 092-XXXX-145
       {12336,29555,37008}, // 092-XXXX-151
       {30326,24158, 6425}, // 092-XXXX-157
       {63479,63479,63479}, // 092-XXXX-123
       {63479,63479,63479}  // 092-XXXX-123
   },
   { // This color scheme is (very loosely) inspired by the first version of the PDP-11/70.
     // Many RGB values came from: http://www.chdickman.com/pdp8/DECcolors/
       {63479,63479,63479}, // 092-XXXX-123
       { 5140, 2056, 5654}, // 092-XXXX-152
       {51400,34952,26682}, // homemade, derived from 092-XXXX-136
       {20000,13107,12850}, // homemade, derived from 092-XXXX-154
       {65535,13107,12850}, // homemade, derived from 092-XXXX-154
       {20000,13107,12850}, // homemade, derived from 092-XXXX-154
       {28270, 8995,19532}, // 092-XXXX-140
       {40092,11051,15677}, // 092-XXXX-139
       {15000,21000, 4000}, // homemade, derived from 092-XXXX-129
       {63479,63479,63479}, // 092-XXXX-123
       {63479,63479,63479}  // 092-XXXX-123
   }
};

/* -------------------------------------------------------------------------- */
/* Helper Functions                                                           */
/* -------------------------------------------------------------------------- */

// Fill in boilerplate when selecting colors.
#define COLOR(X) &color_list[nedsim->color_index].X

// Set foreground color for the current graphics context.
static void
set_color(struct NEDsim * nedsim, struct color_rgb * color)
{
   XColor temp;
   XWindowAttributes xgwa;

   XGetWindowAttributes(nedsim->dpy, nedsim->win, &xgwa);

   temp.red = color->red;
   temp.green = color->green;
   temp.blue = color->blue;

   XAllocColor(nedsim->dpy, xgwa.colormap, &temp);
   XSetForeground(nedsim->dpy, nedsim->gc, temp.pixel);
}

// TODO: Make this a lot faster.
// Set font size to fill 'size' cells vertically, minus space for border and padding.
static void
set_font_size(struct NEDsim * nedsim, int size)
{
   //                                                          vvv--- for border ---vvv    vvv--- for padding ---vvv
   int desired_height_in_pixels = (size * nedsim->cell_size) - (2 * nedsim->border_size) - (8 * nedsim->border_size);

   const char * font_size_prefix = "-*-helvetica-*-r-*-*-";
   const char * font_size_suffix = "-*-*-*-*-*-*-*";

   size_t buffer_size = strlen(font_size_prefix) + strlen(font_size_suffix) + 100; // '100' since nobody needs font with size in 'points' greater than 100 decimal digits long.
   char * font_full_name = malloc(buffer_size);
   int font_size_in_points = 2; // Start with a 2 pt font and work our way up.

   while (1) {
       // Load the font.
       snprintf(font_full_name, buffer_size, "%s%d%s", font_size_prefix, font_size_in_points, font_size_suffix);
       XFontStruct * font = XLoadQueryFont(nedsim->dpy, font_full_name);
       if (!font) {
           printf("WARNING: Unable to load font %s. Probably gonna look wonky.\n", font_full_name);
           font = XLoadQueryFont(nedsim->dpy, "fixed");
           break;
       }
       XSetFont(nedsim->dpy, nedsim->gc, font->fid);

       // Get the height.
       int direction, ascent, descent;
       XCharStruct overall;
       XTextExtents(font, "X", 1, &direction, &ascent, &descent, &overall);

       // Compare the height.
       int height = overall.ascent - overall.descent;
       if (height == desired_height_in_pixels) {
           break;
       } else if (height > desired_height_in_pixels) { 
           font_size_in_points--;
           snprintf(font_full_name, buffer_size, "%s%d%s", font_size_prefix, font_size_in_points, font_size_suffix);
           XFontStruct * font = XLoadQueryFont(nedsim->dpy, font_full_name);
           if (!font) {
               printf("WARNING: Unable to load font %s. Probably gonna look wonky.\n", font_full_name);
               font = XLoadQueryFont(nedsim->dpy, "fixed");
               break;
           }
           XSetFont(nedsim->dpy, nedsim->gc, font->fid);
           break;
       } else {
           font_size_in_points++;
       }
   }

   free(nedsim->current_font);
   nedsim->current_font = font_full_name;
}

// Unlike most functions in this program that input/output in units of 'cells',
// this function uses units of 'pixels' so the caller can track fractional cell
// usage (e.g. for centering the text).
static void
get_text_size(struct NEDsim * nedsim, const char * text, int * x_size, int * y_size)
{
   int direction, ascent, descent;
   XCharStruct overall;
   XFontStruct * font = XLoadQueryFont(nedsim->dpy, nedsim->current_font);
   XTextExtents(font, text, strlen(text), &direction, &ascent, &descent, &overall);
   *x_size = overall.width;
   *y_size = overall.ascent - overall.descent;
}

// When specifying the rectangular area to draw, all coordinates and sizes are
// in units of 'cells'.  Also, be aware that this function alters the
// foreground color.
static void
draw_rect_area(struct NEDsim * nedsim, size_t x_origin, size_t y_origin, size_t x_size, size_t y_size,
              Bool bord_top, Bool bord_bottom, Bool bord_left, Bool bord_right)
{
   // First fill in the rectangular area...
   x_origin *= nedsim->cell_size;
   x_origin += nedsim->origin_x_offset;
   y_origin *= nedsim->cell_size;
   y_origin += nedsim->origin_y_offset;
   x_size *= nedsim->cell_size;
   y_size *= nedsim->cell_size;
   XFillRectangle(nedsim->dpy, nedsim->panel, nedsim->gc, x_origin, y_origin, x_size, y_size);

   // ...then give it a border, if requested.
   set_color(nedsim, COLOR(border));
   if (bord_top) {
       XFillRectangle(nedsim->dpy, nedsim->panel, nedsim->gc,
               x_origin, y_origin, x_size, nedsim->border_size);
   }
   if (bord_bottom) {
       XFillRectangle(nedsim->dpy, nedsim->panel, nedsim->gc,
               x_origin, (y_origin + y_size - nedsim->border_size), x_size, nedsim->border_size);
   }
   if (bord_left) {
       XFillRectangle(nedsim->dpy, nedsim->panel, nedsim->gc,
               x_origin, y_origin, nedsim->border_size, y_size);
   }
   if (bord_right) {
       XFillRectangle(nedsim->dpy, nedsim->panel, nedsim->gc,
               (x_origin + x_size - nedsim->border_size), y_origin, nedsim->border_size, y_size);
   }
}

// Draws filled circle in a square area with upper left corner at x,y.  When
// specifying the location and size to draw, all values are in units of
// 'cells'.  Also, be aware that this function alters the foreground color.
static void
draw_circular_area(struct NEDsim * nedsim, size_t x, size_t y, double diameter)
{
   // First, convert the function argument units from 'cells' to 'pixels'
   x *= nedsim->cell_size;
   y *= nedsim->cell_size;
   diameter *= nedsim->cell_size;

   // Add the panel's absolute x,y offset to the requested coordinates.
   x += nedsim->origin_x_offset;
   y += nedsim->origin_y_offset;

   // Shrink the circle to be a bit smaller than the bounding box allows. Note
   // that the three adjustment values must sum to 1.0.
   // For example, 0.7 + 0.15 + 0.15 = 1.0.
   x += (0.15 * diameter);
   y += (0.15 * diameter);
   diameter *= 0.7;

   // Because we only draw the bottom border on repeated rows (e.g. draw_wordline()),
   // we need to offset vertically by half a border height.
   y -= (0.5 * nedsim->border_size);

   // Start angle 0 and ending angle 360*64 is one full circle in Xlib units.
   XFillArc(nedsim->dpy, nedsim->panel, nedsim->gc, x, y, diameter, diameter, 0, 360*64);
}

// Draws text in a square area with upper left corner at (x_origin,y_origin).
// Requires that set_font_size() has been run at least once. All values are in
// units of 'cells'.
static void
draw_text(struct NEDsim * nedsim, const char * text, int x_origin, int y_origin, int x_size, int y_size, Bool horizontally_center)
{
   set_color(nedsim, COLOR(text));

   int text_x_size, text_y_size;
   get_text_size(nedsim, text, &text_x_size, &text_y_size);

   int local_y_offset = ((y_size * nedsim->cell_size) - text_y_size) / 2;
   int local_x_offset = 0;
   if (horizontally_center) local_x_offset = ((x_size * nedsim->cell_size) - text_x_size) / 2;

   XDrawString(nedsim->dpy, nedsim->panel, nedsim->gc, (x_origin * nedsim->cell_size + nedsim->origin_x_offset + local_x_offset),
           ((y_origin + y_size) * nedsim->cell_size + nedsim->origin_y_offset - local_y_offset), text, strlen(text));
}

// Draws the panel itself. Not the lights/labels/etc, but the flat sheet of
// metal that is the front panel.
static void
draw_panel(struct NEDsim * nedsim)
{
   // Draw background color over entire window.
   set_color(nedsim, COLOR(panel_bg));
   XFillRectangle(nedsim->dpy, nedsim->panel, nedsim->gc, 0, 0, nedsim->dpy_width, nedsim->dpy_height);

   // Draw NED panel in foreground color.
   set_color(nedsim, COLOR(panel_fg));
   XFillRectangle(nedsim->dpy, nedsim->panel, nedsim->gc,
           nedsim->origin_x_offset,
           nedsim->origin_y_offset,
           nedsim->cell_size * OVERALL_WIDTH_IN_CELLS,
           nedsim->cell_size * (HEADER_HEIGHT_IN_CELLS + nedsim->num_data_rows + FOOTER_HEIGHT_IN_CELLS)
   );

   // Give the panel rounded corners by first deleting the four right-angle corners...
   set_color(nedsim, COLOR(panel_bg));
   XFillRectangle(nedsim->dpy, nedsim->panel, nedsim->gc,
           nedsim->origin_x_offset,
           nedsim->origin_y_offset,
           nedsim->cell_size,
           nedsim->cell_size
   );
   XFillRectangle(nedsim->dpy, nedsim->panel, nedsim->gc,
           nedsim->origin_x_offset + (nedsim->cell_size * (OVERALL_WIDTH_IN_CELLS-1)),
           nedsim->origin_y_offset,
           nedsim->cell_size,
           nedsim->cell_size
   );
   XFillRectangle(nedsim->dpy, nedsim->panel, nedsim->gc,
           nedsim->origin_x_offset,
           nedsim->origin_y_offset + (nedsim->cell_size * (HEADER_HEIGHT_IN_CELLS + nedsim->num_data_rows + FOOTER_HEIGHT_IN_CELLS - 1)),
           nedsim->cell_size,
           nedsim->cell_size
   );
   XFillRectangle(nedsim->dpy, nedsim->panel, nedsim->gc,
           nedsim->origin_x_offset + (nedsim->cell_size * (OVERALL_WIDTH_IN_CELLS-1)),
           nedsim->origin_y_offset + (nedsim->cell_size * (HEADER_HEIGHT_IN_CELLS + nedsim->num_data_rows + FOOTER_HEIGHT_IN_CELLS - 1)),
           nedsim->cell_size,
           nedsim->cell_size
   );
   // ...and then replacing them with filled arcs, forming rounded corners.
   set_color(nedsim, COLOR(panel_fg));
   XFillArc(nedsim->dpy, nedsim->panel, nedsim->gc,
           nedsim->origin_x_offset,
           nedsim->origin_y_offset,
           nedsim->cell_size * 2, nedsim->cell_size * 2,
           180*64, -90*64
   );
   XFillArc(nedsim->dpy, nedsim->panel, nedsim->gc,
           nedsim->origin_x_offset + (nedsim->cell_size * (OVERALL_WIDTH_IN_CELLS-2)),
           nedsim->origin_y_offset,
           nedsim->cell_size * 2, nedsim->cell_size * 2,
           0, 90*64
   );
   XFillArc(nedsim->dpy, nedsim->panel, nedsim->gc,
           nedsim->origin_x_offset,
           nedsim->origin_y_offset + (nedsim->cell_size * (HEADER_HEIGHT_IN_CELLS + nedsim->num_data_rows + FOOTER_HEIGHT_IN_CELLS - 2)),
           nedsim->cell_size * 2, nedsim->cell_size * 2,
           180*64, 90*64
   );
   XFillArc(nedsim->dpy, nedsim->panel, nedsim->gc,
           nedsim->origin_x_offset + (nedsim->cell_size * (OVERALL_WIDTH_IN_CELLS-2)),
           nedsim->origin_y_offset + (nedsim->cell_size * (HEADER_HEIGHT_IN_CELLS + nedsim->num_data_rows + FOOTER_HEIGHT_IN_CELLS - 2)),
           nedsim->cell_size * 2, nedsim->cell_size * 2,
           0, -90*64
   );
}

// Draw the "NED" and "subgeniuskitty.com" logos on the front panel.
static void
draw_logo(struct NEDsim * nedsim)
{
   // First draw the two colored boxes that comprise the logo area.
   set_color(nedsim, COLOR(primary));
   draw_rect_area(nedsim, LOGO_X_OFFSET, LOGO_Y_OFFSET, LOGO_WIDTH, LOGO_NAME_HEIGHT, True, True, False, False);
   set_color(nedsim, COLOR(tertiary));
   draw_rect_area(nedsim, LOGO_X_OFFSET, LOGO_Y_OFFSET+LOGO_NAME_HEIGHT, LOGO_WIDTH, LOGO_WEBSITE_HEIGHT, False, True, False, False);

   // Now draw the 'NED' text in the top box.
   set_font_size(nedsim, LOGO_NAME_HEIGHT);
   draw_text(nedsim, "NED", LOGO_X_OFFSET, LOGO_Y_OFFSET, LOGO_WIDTH, LOGO_NAME_HEIGHT, True);

   // And draw the 'subgeniuskitty.com' text in the bottom box.
   set_font_size(nedsim, LOGO_WEBSITE_HEIGHT);
   draw_text(nedsim, "subgeniuskitty.com", LOGO_X_OFFSET, LOGO_Y_OFFSET+LOGO_NAME_HEIGHT, LOGO_WIDTH, LOGO_WEBSITE_HEIGHT, True);
}

// Draw the HALT indicator area on the front panel.
static void
draw_halt(struct NEDsim * nedsim)
{
   // First draw the two colored boxes that comprise the halt area.
   set_color(nedsim, COLOR(tertiary));
   draw_rect_area(nedsim, HALT_X_OFFSET, HALT_Y_OFFSET, HALT_WIDTH, HALT_LIGHT_HEIGHT, True, True, False, False);
   set_color(nedsim, COLOR(secondary));
   draw_rect_area(nedsim, HALT_X_OFFSET, HALT_Y_OFFSET+HALT_LIGHT_HEIGHT, HALT_WIDTH, HALT_LABEL_HEIGHT, False, True, False, False);

   // And finally, draw the label.
   draw_text(nedsim, "HALT", HALT_X_OFFSET, HALT_Y_OFFSET+HALT_LIGHT_HEIGHT, HALT_WIDTH, HALT_LABEL_HEIGHT, True);
}

// Draw the 32 lights corresponding to 'word' at coordinates ('x','y').
// Note that this function ONLY draws the lights and is used each frame for
// updating the panel. To draw the wordline area itself, use draw_wordline().
static void
draw_wordline_lights(struct NEDsim * nedsim, uint32_t word, int x, int y)
{
   for (int i = 0; i < WORDLINE_WIDTH; i++) {
       if (word & (1<<(WORDLINE_WIDTH-1-i))) {
           set_color(nedsim, COLOR(light_on));
       } else {
           set_color(nedsim, COLOR(light_off));
       }
       draw_circular_area(nedsim, x+i, y, WORDLINE_HEIGHT);
   }
}

// Draw a single 32-bit NED word line at coordinates ('x','y').
// Note that this draws a wordline with value 0. To update with a specific
// value, call draw_wordline_lights() after drawing the wordline area at least
// once.
static void
draw_wordline(struct NEDsim * nedsim, int x, int y)
{
   // First, draw a solid box in the primary color over the entire wordline area.
   set_color(nedsim, COLOR(primary));
   draw_rect_area(nedsim, x, y, WORDLINE_WIDTH, WORDLINE_HEIGHT, False, True, False, False);

   // Now, draw stripes in the secondary color.
   int i;
   for (i = 0; i < (WORDLINE_WIDTH/(2*WORDLINE_BITS_PER_STRIPE)); i++) {
       set_color(nedsim, COLOR(secondary));
       draw_rect_area(nedsim, (x+(i*(WORDLINE_WIDTH/WORDLINE_BITS_PER_STRIPE))), y,
               WORDLINE_BITS_PER_STRIPE, WORDLINE_HEIGHT, False, True, False, False);
   }

   // Finally, draw the lights.
   draw_wordline_lights(nedsim, 0, x, y);
}

// Draw the Program Counter area (but don't populate it yet).
static void
draw_pc(struct NEDsim * nedsim)
{
   // First draw the two colored boxes that comprise the PC area.
   set_color(nedsim, COLOR(tertiary));
   draw_rect_area(nedsim, PC_X_OFFSET, PC_Y_OFFSET, PC_WIDTH, PC_LABEL_HEIGHT, True, True, False, False);
   draw_wordline(nedsim, PC_X_OFFSET, PC_Y_OFFSET+PC_LABEL_HEIGHT);

   // Now draw the label text "PC".
   draw_text(nedsim, "PC", PC_X_OFFSET, PC_Y_OFFSET, PC_WIDTH, PC_LABEL_HEIGHT, True);
}

// Draw the Stack Counter area (but don't populate it yet).
static void
draw_sc(struct NEDsim * nedsim)
{
   // First draw the two colored boxes that comprise the SC area.
   set_color(nedsim, COLOR(secondary));
   draw_rect_area(nedsim, SC_X_OFFSET, SC_Y_OFFSET, SC_WIDTH, SC_LABEL_HEIGHT, True, True, False, False);
   set_color(nedsim, COLOR(tertiary));
   draw_rect_area(nedsim, SC_X_OFFSET, SC_Y_OFFSET+SC_LABEL_HEIGHT, SC_WIDTH, SC_LIGHT_HEIGHT, False, True, False, False);

   // Now draw the label text "SC".
   draw_text(nedsim, "SC", SC_X_OFFSET, SC_Y_OFFSET, SC_WIDTH, SC_LABEL_HEIGHT, True);
}

// Draw areas for the two PSW flags, 'Z'ero and 'N'egative.
static void
draw_psw(struct NEDsim * nedsim)
{
   // First draw the four colored boxes that comprise the two PSW areas.
   set_color(nedsim, COLOR(secondary));
   draw_rect_area(nedsim, PSW_N_X_OFFSET, PSW_Y_OFFSET, PSW_LABEL_WIDTH, PSW_LABEL_HEIGHT, True, True, False, False);
   set_color(nedsim, COLOR(secondary));
   draw_rect_area(nedsim, PSW_Z_X_OFFSET, PSW_Y_OFFSET, PSW_LABEL_WIDTH, PSW_LABEL_HEIGHT, True, True, False, False);
   set_color(nedsim, COLOR(tertiary));
   draw_rect_area(nedsim, (PSW_N_X_OFFSET + 1), PSW_Y_OFFSET+PSW_LABEL_HEIGHT, PSW_LIGHT_WIDTH, PSW_LIGHT_HEIGHT, False, True, False, False);
   set_color(nedsim, COLOR(tertiary));
   draw_rect_area(nedsim, (PSW_Z_X_OFFSET + 1), PSW_Y_OFFSET+PSW_LABEL_HEIGHT, PSW_LIGHT_WIDTH, PSW_LIGHT_HEIGHT, False, True, False, False);

   // Now draw the label text.
   draw_text(nedsim, "N", PSW_N_X_OFFSET, PSW_Y_OFFSET, PSW_LABEL_WIDTH, PSW_LABEL_HEIGHT, True);
   draw_text(nedsim, "Z", PSW_Z_X_OFFSET, PSW_Y_OFFSET, PSW_LABEL_WIDTH, PSW_LABEL_HEIGHT, True);
}

// Draw the stack area (but don't populate it yet).
static void
draw_stack(struct NEDsim * nedsim)
{
   // First draw the two colored boxes that comprise the stack area.
   set_color(nedsim, COLOR(tertiary));
   draw_rect_area(nedsim, STACK_X_OFFSET, STACK_Y_OFFSET, STACK_WIDTH, STACK_LABEL_HEIGHT, True, True, False, False);
   for (int i = 0; i < nedsim->num_data_rows; i++) {
       draw_wordline(nedsim, STACK_X_OFFSET, STACK_Y_OFFSET+STACK_LABEL_HEIGHT+i);
   }

   // Now draw the label text "Stack Size:".
   draw_text(nedsim, "Stack Size:", STACK_X_OFFSET+1, STACK_Y_OFFSET, STACK_WIDTH, STACK_LABEL_HEIGHT, False);
}

// Draw the heap area (but don't populate it yet).
static void
draw_heap(struct NEDsim * nedsim)
{
// TODO: What should I do about this define? I would like to be able to specify the address so I can do things like display the code itself if nothign interesting happens in RAM.
#define HEAP_START_ADDRESS 0x20000000

   // First draw the two colored boxes that comprise the heap area.
   set_color(nedsim, COLOR(tertiary));
   draw_rect_area(nedsim, HEAP_X_OFFSET, HEAP_Y_OFFSET, HEAP_WIDTH, HEAP_LABEL_HEIGHT, True, True, False, False);
   for (int i = 0; i < nedsim->num_data_rows; i++) {
       draw_wordline(nedsim, HEAP_X_OFFSET, HEAP_Y_OFFSET+HEAP_LABEL_HEIGHT+i);
   }

   // Now draw the text label "RAM Base:".
   draw_text(nedsim, "RAM Base:", HEAP_X_OFFSET+1, HEAP_Y_OFFSET, HEAP_WIDTH, HEAP_LABEL_HEIGHT, False);

   // Now draw the address text.
   char address[11];
   snprintf(address, sizeof(address), "0x%08X", HEAP_START_ADDRESS);
   draw_text(nedsim, address, (HEAP_X_OFFSET+(HEAP_WIDTH/2)+1), HEAP_Y_OFFSET, HEAP_WIDTH, HEAP_LABEL_HEIGHT, False);
}

// After the static front panel has been drawn at least once, this function
// updates all the dynamic parts of the panel (lights + text values) and is
// called every frame.
static void
update_display(struct NEDsim * nedsim)
{
   // Draw the halt indicator.
   if (nedsim->nedstate->halted) {
       set_color(nedsim, COLOR(error_on));
   } else {
       set_color(nedsim, COLOR(error_off));
   }
   draw_circular_area(nedsim, HALT_X_OFFSET, HALT_Y_OFFSET, HALT_WIDTH);

   // Draw the PSW "N" light.
   if (nedsim->nedstate->active_thread->psw->negative) {
       set_color(nedsim, COLOR(light_on));
   } else {
       set_color(nedsim, COLOR(light_off));
   }
   draw_circular_area(nedsim, PSW_N_X_OFFSET+1, PSW_Y_OFFSET+PSW_LABEL_HEIGHT, PSW_LIGHT_HEIGHT);

   // Draw the PSW "Z" light.
   if (nedsim->nedstate->active_thread->psw->zero) {
       set_color(nedsim, COLOR(light_on));
   } else {
       set_color(nedsim, COLOR(light_off));
   }
   draw_circular_area(nedsim, PSW_Z_X_OFFSET+1, PSW_Y_OFFSET+PSW_LABEL_HEIGHT, PSW_LIGHT_HEIGHT);


   // Draw the SC.
   int i;
   for (i = 0; i < SC_WIDTH; i++) {
       if ((SC_WIDTH-1-i) == nedsim->nedstate->active_thread->sc) {
           set_color(nedsim, COLOR(light_on));
       } else {
           set_color(nedsim, COLOR(light_off));
       }
       draw_circular_area(nedsim, SC_X_OFFSET+i, SC_Y_OFFSET+SC_LABEL_HEIGHT, SC_LIGHT_HEIGHT);
   }

   // Draw the PC.
   draw_wordline_lights(nedsim, nedsim->nedstate->active_thread->pc, PC_X_OFFSET, PC_Y_OFFSET+PC_LABEL_HEIGHT);

   // Draw the stack lights.
   int64_t top_of_stack = ((int64_t)nedsim->nedstate->active_thread->sp) - 1;
   for (i = 0; i < nedsim->num_data_rows; i++) {
       if ((top_of_stack-i) >= 0) {
           draw_wordline_lights(nedsim, nedsim->nedstate->active_thread->stack[top_of_stack-i], STACK_X_OFFSET, STACK_Y_OFFSET+STACK_LABEL_HEIGHT+i);
       } else {
           draw_wordline_lights(nedsim, 0, STACK_X_OFFSET, STACK_Y_OFFSET+STACK_LABEL_HEIGHT+i);
       }
   }

   // Draw the stack size in text.
   set_color(nedsim, COLOR(tertiary));
   draw_rect_area(nedsim, STACK_X_OFFSET+(STACK_WIDTH/2), STACK_Y_OFFSET, STACK_WIDTH/2, STACK_LABEL_HEIGHT, True, True, False, False);
   char stack_size[11];
   snprintf(stack_size, sizeof(stack_size), "0x%08X", nedsim->nedstate->active_thread->sp);
   draw_text(nedsim, stack_size, (STACK_X_OFFSET+(STACK_WIDTH/2)+1), STACK_Y_OFFSET, STACK_WIDTH, STACK_LABEL_HEIGHT, False);

   // Draw the heap lights.
   for (i = 0; i < nedsim->num_data_rows; i++) {
       draw_wordline_lights(nedsim, ram_r_word(nedsim->nedstate, HEAP_START_ADDRESS+(i*BPW)), HEAP_X_OFFSET, HEAP_Y_OFFSET+HEAP_LABEL_HEIGHT+i);
   }
}

/* -------------------------------------------------------------------------- */
/* Screenhack API Functions                                                   */
/* -------------------------------------------------------------------------- */

static Bool
NEDsim_event(Display * dpy, Window win, void * closure, XEvent * event)
{
   return False;
}

static void
NEDsim_free(Display * dpy, Window win, void * closure)
{
   struct NEDsim * nedsim = closure;

   if (nedsim->nedstate != NULL) {
       free(nedsim->nedstate->active_thread->psw);
       free(nedsim->nedstate->active_thread);
       free(nedsim->nedstate->hack);
       free(nedsim->nedstate);
   }

   // TODO: Replace all this with proper code to free everything related to the screensaver itself.
   XFreeGC(nedsim->dpy, nedsim->gc);
   XFreePixmap(nedsim->dpy, nedsim->panel);
   free(nedsim);
}

static void *
NEDsim_init(Display * dpy, Window win)
{
   // =========================================================================
   //  Basic Setup
   // =========================================================================

   struct NEDsim * nedsim;

   nedsim = calloc(1, sizeof(*nedsim));
   if (!nedsim) {
       fprintf(stderr, "ERROR: Failed to calloc() for NEDsim struct in NEDsim_init().\n");
       exit(EXIT_FAILURE);
   }

   nedsim->dpy = dpy;
   nedsim->win = win;

   XGCValues gcv;
   nedsim->gc = XCreateGC(nedsim->dpy, nedsim->win, GCForeground, &gcv);

   XWindowAttributes xgwa;
   XGetWindowAttributes(nedsim->dpy, nedsim->win, &xgwa);
   nedsim->dpy_width = xgwa.width;
   nedsim->dpy_height = xgwa.height;

   nedsim->panel = XCreatePixmap(nedsim->dpy, nedsim->win, nedsim->dpy_width, nedsim->dpy_height, xgwa.depth);

   // =========================================================================
   //  Process User Requests
   // =========================================================================

   nedsim->delay = get_integer_resource(nedsim->dpy, "delay", "Integer");
   nedsim->delay *= 1000; /* Turn milliseconds into microseconds. */

   // If the user did not supply a program for execution, randomly select one
   // of the included programs.
   char * input_file = get_string_resource(nedsim->dpy, "binary", "String");
   if (input_file == NULL) {
       // TODO: Need to include some default programs and randomly select one to load into RAM.
       nedsim->nedstate = init_simulator("./test.out");
   } else {
       nedsim->nedstate = init_simulator(input_file);
   }

   // If the user did not select a color scheme, select one randomly.
   nedsim->color_index = get_integer_resource(nedsim->dpy, "color", "Integer");
   if (nedsim->color_index == -1) {
       nedsim->color_index = random() % sizeof(color_list)/sizeof(color_list[0]);
   } else if (nedsim->color_index >= sizeof(color_list)/sizeof(color_list[0])) {
       fprintf(stderr, "WARNING: Color index out of range.\n");
       nedsim->color_index = 0;
   }

   // =========================================================================
   //  Scale Panel To Screen
   // =========================================================================

   // We desire to make the panel as wide as possible while also making the
   // cell size an integer pixel size.
   nedsim->cell_size = nedsim->dpy_width / OVERALL_WIDTH_IN_CELLS;
   // Cell sizes below about 10 pixels result in unreadable fonts. For now,
   // we'll use that as our cutoff. It also works well with a 1:10 border:cell
   // ratio.
   if (nedsim->cell_size < 10) {
       nedsim->suitable_display = False;
       return nedsim;
   }
   // Center the panel horizontally.
   nedsim->origin_x_offset = (nedsim->dpy_width -
           (nedsim->cell_size * OVERALL_WIDTH_IN_CELLS)) / 2;

   // The stack and heap displays are variable height. Size them to fit the
   // display window.
   int available_space_for_data_rows = nedsim->dpy_height -
           (nedsim->cell_size * (HEADER_HEIGHT_IN_CELLS + FOOTER_HEIGHT_IN_CELLS));
   for (int i = 0; ; i++) {
       if ((nedsim->cell_size * i) > available_space_for_data_rows) {
           nedsim->num_data_rows = --i;
           break;
       }
   }
   // Enforce a minimum vertical size, though '4' is arbitrary.
   if (nedsim->num_data_rows < 4) {
       nedsim->suitable_display = False;
       return nedsim;
   }
   // Center the panel vertically.
   nedsim->origin_y_offset = (nedsim->dpy_height -
           (nedsim->cell_size * (HEADER_HEIGHT_IN_CELLS + nedsim->num_data_rows + FOOTER_HEIGHT_IN_CELLS))) / 2;

   // Scale border relative to cell_size in a 1:10 relationship.
   nedsim->border_size = nedsim->cell_size / 10;

   // =========================================================================
   //  Draw Initial Panel
   // =========================================================================

   draw_panel(nedsim);
   draw_logo(nedsim);
   draw_halt(nedsim);
   draw_pc(nedsim);
   draw_sc(nedsim);
   draw_psw(nedsim);
   draw_stack(nedsim);
   draw_heap(nedsim);

   nedsim->suitable_display = True;

   return nedsim;
}

static unsigned long
NEDsim_draw(Display * dpy, Window win, void * closure)
{
   struct NEDsim * nedsim = closure;

   // Update the panel display buffer.
   if (nedsim->suitable_display) {
       nedsim->nedstate = run_simulator(nedsim->nedstate);
       update_display(nedsim);
   } else {
       set_color(nedsim, COLOR(error_on));
       XFillRectangle(nedsim->dpy, nedsim->panel, nedsim->gc, 0, 0, nedsim->dpy_width, nedsim->dpy_height);
   }

   // Copy panel buffer to display window.
   XCopyArea(nedsim->dpy, nedsim->panel, nedsim->win, nedsim->gc, 0, 0, nedsim->dpy_width, nedsim->dpy_height, 0, 0);

   return nedsim->delay;
}

static void
NEDsim_reshape(Display * dpy, Window win, void * closure, unsigned int w, unsigned int h)
{
   struct NEDsim * nedsim = closure;

   // Only re-initialize the display if it changed size.
   XWindowAttributes xgwa;
   XGetWindowAttributes(nedsim->dpy, nedsim->win, &xgwa);
   if (nedsim->dpy_width != xgwa.width || nedsim->dpy_height != xgwa.height) {
       // Although we are re-initializing the display, we wish to retain the
       // in-progress NED simulation. Thus, we retain the NEDstate pointer.
       struct NEDstate * original_nedstate = nedsim->nedstate;
       nedsim->nedstate = NULL;
       NEDsim_free(dpy, win, nedsim);
       struct NEDsim * new_nedsim = NEDsim_init(dpy, win);
       new_nedsim->nedstate = original_nedstate;
       closure = new_nedsim;
   }
}

static const char * NEDsim_defaults[] = {
   "*delay:              250",
   "*color:               -1",
   0
};

static XrmOptionDescRec NEDsim_options[] = {
   { "-delay",              ".delay",                  XrmoptionSepArg, 0      },
   { "-binary",             ".binary",                 XrmoptionSepArg, 0      },
   { "-color",              ".color",                  XrmoptionSepArg, 0      },
   { 0, 0, 0, 0 }
};

XSCREENSAVER_MODULE ("Blinken-lights simulator for NED1 CPU architecture.", NEDsim)