Initial commit of NED1 front panel code I've been hacking on.

[screensavers] / hacks / NEDsim / NEDsim.c

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

// TODO:
//      - Write a brief description of the machine being simulated. Only one thread, reduced RAM, no meaningful console when running as screensaver, etc.

// CLI Flags:
//      -path-to-aout-binary
//      -path-to-font-file
//      -speed

// Ideas for sample programs to include:
//      - Build list of integers on the stack (DUP, IM_1, ADD).
//      - Calculate prime numbers, placing them on the stack.
//      - Lights sliding back and forth, like PDP-11 front panel with some OSes.

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

/* Keep this source code C89 compliant per XScreensaver's instructions.       */

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

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

    // TODO: Explain these
    int dpy_width, dpy_height;

    // TODO: Explain that this is created during init, then lights are populated/overwritten on each frame. 
    Pixmap panel;

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

    int cell_size;
    int border_size;
    int origin_x_offset, origin_y_offset;
    int num_data_rows;

    size_t color_index;

    Bool suitable_display;

    char * current_font;

    // TODO: Explain that this contains all the actual state of the NED machine being simulated.
    struct NEDstate * nedstate;
};

struct color_rgb {
    // TODO: Explain why this is an unsigned short. Copy from WolframAutomata.
    unsigned short red, green, blue;
};

struct color_scheme {
    // TODO: Explain all this.
    struct color_rgb
        panel_bg,
        panel_fg,
        light_on,
        light_off,
        error_on,
        error_off,
        primary,
        secondary,
        tertiary,
        border,
        text;
};

//static struct color_scheme color_list[] = {
//    // TODO: Explain all this.
//    // TODO: Add other color schemes, like purple PDP-11/70.
//    // TODO: http://www.chdickman.com/pdp8/DECcolors/
//    {
//        {63479,63479,63479}, // 092-XXXX-123
//        { 5140, 2056, 5654}, // 092-XXXX-152
//        {40092,11051,15677}, // 092-XXXX-139
//        {30326,13107,12850}, // 092-XXXX-154
//        {65535,13107,12850}, // homemade
//        {30326,13107,12850}, // 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
//    }
//};

static struct color_scheme color_list[] = {
    // TODO: Explain all this.
    // TODO: Add other color schemes, like purple PDP-11/70.
    // TODO: http://www.chdickman.com/pdp8/DECcolors/
    {
        {63479,63479,63479}, // 092-XXXX-123
        { 5140, 2056, 5654}, // 092-XXXX-152
        {65535,11051,15677}, // 092-XXXX-139 - edit
        {20000,13107,12850}, // 092-XXXX-154 - edit
        {65535,13107,12850}, // homemade
        {20000,13107,12850}, // 092-XXXX-154 - edit
        { 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
    }
};

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

// TODO: Explain
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: Explain
// TODO: Make this a lot faster.
// Input: size in 'cells', and sets font to fill that size, minus border and padding room.
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;
}

// TODO: Explain
// TODO: Explain that this returns result in pixels so we can track fractional cell usage.
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;
}

// TODO: Explain
// TODO: Note that this might leave the foreground color changed.
// Argument coordinates are in 'cells', not pixels.
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)
{
    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->win, nedsim->gc, x_origin, y_origin, x_size, y_size);

    set_color(nedsim, &color_list[nedsim->color_index].border);
    if (bord_top) {
        XFillRectangle(nedsim->dpy, nedsim->win, nedsim->gc, x_origin, y_origin, x_size, nedsim->border_size);
    }
    if (bord_bottom) {
        XFillRectangle(nedsim->dpy, nedsim->win, nedsim->gc, x_origin, (y_origin + y_size - nedsim->border_size), x_size, nedsim->border_size);
    }
    if (bord_left) {
        XFillRectangle(nedsim->dpy, nedsim->win, nedsim->gc, x_origin, y_origin, nedsim->border_size, y_size);
    }
    if (bord_right) {
        XFillRectangle(nedsim->dpy, nedsim->win, nedsim->gc, (x_origin + x_size - nedsim->border_size), y_origin, nedsim->border_size, y_size);
    }
}

// TODO: Explain
// Arguments are in units of 'cells', not pixels.
// Will leave foreground color changed.
// Draws filled circle with upper left corner at x,y.
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->win, nedsim->gc, x, y, diameter, diameter, 0, 360*64);
}

// TODO: Explain
static void
draw_panel(struct NEDsim * nedsim)
{
// TODO: Collect all relevant #defines somewhere.
#define OVERALL_WIDTH_IN_CELLS 70 
#define HEADER_HEIGHT_IN_CELLS 14
#define FOOTER_HEIGHT_IN_CELLS 2

    // Draw background color over entire window.
    set_color(nedsim, &color_list[nedsim->color_index].panel_bg);
    XFillRectangle(nedsim->dpy, nedsim->win, nedsim->gc, 0, 0, nedsim->dpy_width, nedsim->dpy_height);

    // Draw NED panel in foreground color.
    set_color(nedsim, &color_list[nedsim->color_index].panel_fg);
    XFillRectangle(nedsim->dpy, nedsim->win, 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)
    );
}

// TODO: Explain
static void
draw_logo(struct NEDsim * nedsim)
{
#define LOGO_X_OFFSET       2
#define LOGO_Y_OFFSET       2
#define LOGO_WIDTH          20
#define LOGO_NAME_HEIGHT    6
#define LOGO_WEBSITE_HEIGHT 2

    // First draw the two colored boxes that comprise the logo area.
    set_color(nedsim, &color_list[nedsim->color_index].primary);
    draw_rect_area(nedsim, LOGO_X_OFFSET, LOGO_Y_OFFSET, LOGO_WIDTH, LOGO_NAME_HEIGHT, True, True, False, False);
    set_color(nedsim, &color_list[nedsim->color_index].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_color(nedsim, &color_list[nedsim->color_index].text);
    set_font_size(nedsim, LOGO_NAME_HEIGHT);
    int text_x_size, text_y_size;
    get_text_size(nedsim, "NED", &text_x_size, &text_y_size);
    int local_x_offset = ((LOGO_WIDTH * nedsim->cell_size) - text_x_size) / 2;
    int local_y_offset = ((LOGO_NAME_HEIGHT * nedsim->cell_size) - text_y_size) / 2;
    XDrawString(nedsim->dpy, nedsim->win, nedsim->gc, (LOGO_X_OFFSET * nedsim->cell_size + nedsim->origin_x_offset + local_x_offset),
            ((LOGO_Y_OFFSET+LOGO_NAME_HEIGHT) * nedsim->cell_size + nedsim->origin_y_offset - local_y_offset), "NED", 3);

    // And draw the 'subgeniuskitty.com' text in the bottom box.
    set_font_size(nedsim, LOGO_WEBSITE_HEIGHT);
    get_text_size(nedsim, "subgeniuskitty.com", &text_x_size, &text_y_size);
    local_x_offset = ((LOGO_WIDTH * nedsim->cell_size) - text_x_size) / 2;
    local_y_offset = ((LOGO_WEBSITE_HEIGHT * nedsim->cell_size) - text_y_size) / 2;
    XDrawString(nedsim->dpy, nedsim->win, nedsim->gc, (LOGO_X_OFFSET * nedsim->cell_size + nedsim->origin_x_offset + local_x_offset),
            ((LOGO_Y_OFFSET+LOGO_NAME_HEIGHT+LOGO_WEBSITE_HEIGHT) * nedsim->cell_size + nedsim->origin_y_offset - local_y_offset), "subgeniuskitty.com", 18);
}

// TODO: Explain
static void
draw_halt(struct NEDsim * nedsim)
{
#define HALT_X_OFFSET     26
#define HALT_Y_OFFSET     2
#define HALT_WIDTH        6
#define HALT_LIGHT_HEIGHT 6
#define HALT_LABEL_HEIGHT 2

    // First draw the two colored boxes that comprise the halt area.
    set_color(nedsim, &color_list[nedsim->color_index].tertiary);
    draw_rect_area(nedsim, HALT_X_OFFSET, HALT_Y_OFFSET, HALT_WIDTH, HALT_LIGHT_HEIGHT, True, True, False, False);
    set_color(nedsim, &color_list[nedsim->color_index].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.
    set_color(nedsim, &color_list[nedsim->color_index].text);
    int text_x_size, text_y_size;
    get_text_size(nedsim, "HALT", &text_x_size, &text_y_size);
    int local_x_offset = ((HALT_WIDTH * nedsim->cell_size) - text_x_size) / 2;
    int local_y_offset = ((HALT_LABEL_HEIGHT * nedsim->cell_size) - text_y_size) / 2;
    XDrawString(nedsim->dpy, nedsim->win, nedsim->gc, (HALT_X_OFFSET * nedsim->cell_size + nedsim->origin_x_offset + local_x_offset),
            ((HALT_Y_OFFSET+HALT_LIGHT_HEIGHT+HALT_LABEL_HEIGHT) * nedsim->cell_size + nedsim->origin_y_offset - local_y_offset), "HALT", 4);
}

// TODO: Explain
static void
draw_wordline_lights(struct NEDsim * nedsim, uint32_t word, int x, int y)
{
#define WORDLINE_BITS_PER_STRIPE 4
#define WORDLINE_WIDTH           32
#define WORDLINE_HEIGHT          1

    for (int i = 0; i < WORDLINE_WIDTH; i++) {
        if (word & (1<<(WORDLINE_WIDTH-1-i))) {
            set_color(nedsim, &color_list[nedsim->color_index].light_on);
        } else {
            set_color(nedsim, &color_list[nedsim->color_index].light_off);
        }
        draw_circular_area(nedsim, x+i, y, WORDLINE_HEIGHT);
    }
}

// TODO: Explain
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_list[nedsim->color_index].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_list[nedsim->color_index].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);
}

// TODO: Explain
static void
draw_pc(struct NEDsim * nedsim)
{
// TODO: Note that all #defines use units of 'cells', not 'pixels', etc.
#define PC_X_OFFSET     36
#define PC_Y_OFFSET     7
#define PC_WIDTH        32
#define PC_LABEL_HEIGHT 2
#define PC_LIGHT_HEIGHT 1

    // First draw the two colored boxes that comprise the PC area.
    set_color(nedsim, &color_list[nedsim->color_index].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".
    set_color(nedsim, &color_list[nedsim->color_index].text);
    int text_x_size, text_y_size;
    get_text_size(nedsim, "PC", &text_x_size, &text_y_size);
    int local_x_offset = ((PC_WIDTH * nedsim->cell_size) - text_x_size) / 2;
    int local_y_offset = ((PC_LABEL_HEIGHT * nedsim->cell_size) - text_y_size) / 2;
    XDrawString(nedsim->dpy, nedsim->win, nedsim->gc, (PC_X_OFFSET * nedsim->cell_size + nedsim->origin_x_offset + local_x_offset),
            ((PC_Y_OFFSET+PC_LABEL_HEIGHT) * nedsim->cell_size + nedsim->origin_y_offset - local_y_offset), "PC", 2);
}

// TODO: Explain
static void
draw_sc(struct NEDsim * nedsim)
{
#define SC_X_OFFSET     42
#define SC_Y_OFFSET     2
#define SC_WIDTH        5
#define SC_LABEL_HEIGHT 2
#define SC_LIGHT_HEIGHT 1

    // First draw the two colored boxes that comprise the SC area.
    set_color(nedsim, &color_list[nedsim->color_index].secondary);
    draw_rect_area(nedsim, SC_X_OFFSET, SC_Y_OFFSET, SC_WIDTH, SC_LABEL_HEIGHT, True, True, False, False);
    set_color(nedsim, &color_list[nedsim->color_index].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".
    set_color(nedsim, &color_list[nedsim->color_index].text);
    int text_x_size, text_y_size;
    get_text_size(nedsim, "SC", &text_x_size, &text_y_size);
    int local_x_offset = ((SC_WIDTH * nedsim->cell_size) - text_x_size) / 2;
    int local_y_offset = ((SC_LABEL_HEIGHT * nedsim->cell_size) - text_y_size) / 2;
    XDrawString(nedsim->dpy, nedsim->win, nedsim->gc, (SC_X_OFFSET * nedsim->cell_size + nedsim->origin_x_offset + local_x_offset),
            ((SC_Y_OFFSET+SC_LABEL_HEIGHT) * nedsim->cell_size + nedsim->origin_y_offset - local_y_offset), "SC", 2);
}

// TODO: Explain
static void
draw_psw(struct NEDsim * nedsim)
{
#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

    // First draw the four colored boxes that comprise the two PSW areas.
    set_color(nedsim, &color_list[nedsim->color_index].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_list[nedsim->color_index].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_list[nedsim->color_index].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_list[nedsim->color_index].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 "N".
    set_color(nedsim, &color_list[nedsim->color_index].text);
    int text_x_size, text_y_size;
    get_text_size(nedsim, "N", &text_x_size, &text_y_size);
    int local_x_offset = ((PSW_LABEL_WIDTH * nedsim->cell_size) - text_x_size) / 2;
    int local_y_offset = ((PSW_LABEL_HEIGHT * nedsim->cell_size) - text_y_size) / 2;
    XDrawString(nedsim->dpy, nedsim->win, nedsim->gc, (PSW_N_X_OFFSET * nedsim->cell_size + nedsim->origin_x_offset + local_x_offset),
            ((PSW_Y_OFFSET+PSW_LABEL_HEIGHT) * nedsim->cell_size + nedsim->origin_y_offset - local_y_offset), "N", 1);

    // Now draw the label text "Z".
    set_color(nedsim, &color_list[nedsim->color_index].text);
    get_text_size(nedsim, "Z", &text_x_size, &text_y_size);
    local_x_offset = ((PSW_LABEL_WIDTH * nedsim->cell_size) - text_x_size) / 2;
    local_y_offset = ((PSW_LABEL_HEIGHT * nedsim->cell_size) - text_y_size) / 2;
    XDrawString(nedsim->dpy, nedsim->win, nedsim->gc, (PSW_Z_X_OFFSET * nedsim->cell_size + nedsim->origin_x_offset + local_x_offset),
            ((PSW_Y_OFFSET+PSW_LABEL_HEIGHT) * nedsim->cell_size + nedsim->origin_y_offset - local_y_offset), "Z", 1);
}

// TODO: Explain
static void
draw_stack(struct NEDsim * nedsim)
{
#define STACK_X_OFFSET     2
#define STACK_Y_OFFSET     12
#define STACK_WIDTH        32
#define STACK_LABEL_HEIGHT 2
#define STACK_LIGHT_HEIGHT 1

    // First draw the two colored boxes that comprise the stack area.
    set_color(nedsim, &color_list[nedsim->color_index].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:".
    set_color(nedsim, &color_list[nedsim->color_index].text);
    int text_x_size, text_y_size;
    get_text_size(nedsim, "Stack Size:", &text_x_size, &text_y_size);
    int local_y_offset = ((STACK_LABEL_HEIGHT * nedsim->cell_size) - text_y_size) / 2;
    XDrawString(nedsim->dpy, nedsim->win, nedsim->gc, ((STACK_X_OFFSET + 1) * nedsim->cell_size + nedsim->origin_x_offset),
            ((STACK_Y_OFFSET+STACK_LABEL_HEIGHT) * nedsim->cell_size + nedsim->origin_y_offset - local_y_offset), "Stack Size:", 11);
}

// TODO: Explain
static void
draw_heap(struct NEDsim * nedsim)
{
#define HEAP_X_OFFSET     36
#define HEAP_Y_OFFSET     12
#define HEAP_WIDTH        32
#define HEAP_LABEL_HEIGHT 2
#define HEAP_LIGHT_HEIGHT 1
// 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_list[nedsim->color_index].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 label text "RAM Base:".
    set_color(nedsim, &color_list[nedsim->color_index].text);
    int text_x_size, text_y_size;
    get_text_size(nedsim, "RAM Base:", &text_x_size, &text_y_size);
    int local_y_offset = ((HEAP_LABEL_HEIGHT * nedsim->cell_size) - text_y_size) / 2;
    XDrawString(nedsim->dpy, nedsim->win, nedsim->gc, ((HEAP_X_OFFSET + 1) * nedsim->cell_size + nedsim->origin_x_offset),
            ((HEAP_Y_OFFSET+HEAP_LABEL_HEIGHT) * nedsim->cell_size + nedsim->origin_y_offset - local_y_offset), "RAM Base:", 9);

    // Now draw the address text.
    set_color(nedsim, &color_list[nedsim->color_index].text);
    char address[11];
    snprintf(address, sizeof(address), "0x%08X", HEAP_START_ADDRESS);
    get_text_size(nedsim, address, &text_x_size, &text_y_size);
    local_y_offset = ((HEAP_LABEL_HEIGHT * nedsim->cell_size) - text_y_size) / 2;
    XDrawString(nedsim->dpy, nedsim->win, nedsim->gc, ((HEAP_X_OFFSET + 1 + (HEAP_WIDTH / 2)) * nedsim->cell_size + nedsim->origin_x_offset),
            ((HEAP_Y_OFFSET+HEAP_LABEL_HEIGHT) * nedsim->cell_size + nedsim->origin_y_offset - local_y_offset), address, strlen(address));
}

// TODO: Explain
static void
update_display(struct NEDsim * nedsim)
{
    // Draw the halt indicator.
    if (nedsim->nedstate->halted) {
        set_color(nedsim, &color_list[nedsim->color_index].error_on);
    } else {
        set_color(nedsim, &color_list[nedsim->color_index].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_list[nedsim->color_index].light_on);
    } else {
        set_color(nedsim, &color_list[nedsim->color_index].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_list[nedsim->color_index].light_on);
    } else {
        set_color(nedsim, &color_list[nedsim->color_index].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_list[nedsim->color_index].light_on);
        } else {
            set_color(nedsim, &color_list[nedsim->color_index].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_list[nedsim->color_index].tertiary);
    draw_rect_area(nedsim, STACK_X_OFFSET+(STACK_WIDTH/2), STACK_Y_OFFSET, STACK_WIDTH/2, STACK_LABEL_HEIGHT, True, True, False, False);
    set_color(nedsim, &color_list[nedsim->color_index].text);
    char stack_size[11];
    snprintf(stack_size, sizeof(stack_size), "0x%08X", nedsim->nedstate->active_thread->sp);
    int text_x_size, text_y_size;
    get_text_size(nedsim, stack_size, &text_x_size, &text_y_size);
    int local_y_offset = ((STACK_LABEL_HEIGHT * nedsim->cell_size) - text_y_size) / 2;
    XDrawString(nedsim->dpy, nedsim->win, nedsim->gc, ((STACK_X_OFFSET + 1 + (STACK_WIDTH / 2)) * nedsim->cell_size + nedsim->origin_x_offset),
            ((STACK_Y_OFFSET+STACK_LABEL_HEIGHT) * nedsim->cell_size + nedsim->origin_y_offset - local_y_offset), stack_size, strlen(stack_size));

    // 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)
{
    // TODO: Replace all this with proper code to free everything.
    struct NEDsim * nedsim = closure;
    XFreeGC(nedsim->dpy, nedsim->gc);
    free(nedsim);
}

static void *
NEDsim_init(Display * dpy, Window win)
{
    struct NEDsim * nedsim;
    XGCValues gcv;
    XWindowAttributes xgwa;

    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;

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

    // TODO: Explain that this is the delay between each clock cycle of the simulated NED CPU.
    nedsim->delay = get_integer_resource(nedsim->dpy, "delay", "Integer");
    nedsim->delay *= 1000; /* Turn milliseconds into microseconds. */

    // TODO: Read in the a.out file. This should be done in the simulator's init function call?
    nedsim->nedstate = init_simulator();

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

    // TODO: Do this properly.
    nedsim->color_index = 0;

// TODO: Save the GIMP reference diagram somewhere, along with notes about the size/spacing, and that each cell is 10 pixels across in the reference image.

    nedsim->cell_size = nedsim->dpy_width / OVERALL_WIDTH_IN_CELLS ; // make panel as wide as it can be while keeping every cell an integer pixel size.
    // TODO: What is my minimum cell_size? Below that, I should simply paint the window red and print an error in the console. Perform that check here, right after setting cell_size.
    //       For now, we'll just make it 10 pixels?
    if (nedsim->cell_size < 10) {
        nedsim->suitable_display = False;
        return nedsim;
    }
    nedsim->origin_x_offset = (nedsim->dpy_width - (nedsim->cell_size * OVERALL_WIDTH_IN_CELLS)) / 2; // center panel horizontally

    // Determine how many rows for the stack and heap displays. Make it the largest power of two that fits on the display.
    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 * (1 << i)) > available_space_for_data_rows) {
            nedsim->num_data_rows = (1 << --i);
            break;
        }
    }
    if (nedsim->num_data_rows < 4) {
        nedsim->suitable_display = False;
        return nedsim;
    }
    nedsim->origin_y_offset = (nedsim->dpy_height - (nedsim->cell_size * (HEADER_HEIGHT_IN_CELLS + nedsim->num_data_rows + FOOTER_HEIGHT_IN_CELLS))) / 2; // center panel vertically

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

    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;

    if (nedsim->suitable_display) {
        nedsim->nedstate = run_simulator(nedsim->nedstate);
        update_display(nedsim);
    } else {
        set_color(nedsim, &color_list[nedsim->color_index].error_on);
        XFillRectangle(nedsim->dpy, nedsim->win, nedsim->gc, 0, 0, nedsim->dpy_width, nedsim->dpy_height);
    }

    return nedsim->delay;
}

static void
NEDsim_reshape(Display * dpy, Window win, void * closure, unsigned int w, unsigned int h)
{
    struct NEDsim * nedsim = closure;
    XWindowAttributes xgwa;
    XGetWindowAttributes(nedsim->dpy, nedsim->win, &xgwa);
    /* Only restart the simulation if the window changed size.                */
    if (nedsim->dpy_width != xgwa.width || nedsim->dpy_height != xgwa.height) {
        NEDsim_free(dpy, win, closure);
        closure = NEDsim_init(dpy, win);
    }
}

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

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

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