#version GLSL_VERSION
#define WHICH_PROGRAM
#define NOT_TRANSPARENT
#define DECORATION_SHIFT {DECORATION_SHIFT}
#define REVERSE_SHIFT {REVERSE_SHIFT}
#define STRIKE_SHIFT {STRIKE_SHIFT}
#define DIM_SHIFT {DIM_SHIFT}
#define CURSOR_TEXT_COLOR {CURSOR_TEXT_COLOR}

// Inputs {{{
layout(std140) uniform CellRenderData {
    float xstart, ystart, dx, dy, sprite_dx, sprite_dy, background_opacity;

    uint default_fg, default_bg, highlight_fg, highlight_bg, cursor_color, url_color, url_style, inverted;

    uint xnum, ynum, cursor_fg_sprite_idx;
    float cursor_x, cursor_y, cursor_w;

    uint color_table[256];
};

// Have to use fixed locations here as all variants of the cell program share the same VAO
layout(location=0) in uvec3 colors;
layout(location=1) in uvec4 sprite_coords;
layout(location=2) in uint is_selected;


const int fg_index_map[] = int[3](0, 1, 0);
const uvec2 cell_pos_map[] = uvec2[4](
    uvec2(1, 0),  // right, top
    uvec2(1, 1),  // right, bottom
    uvec2(0, 1),  // left, bottom
    uvec2(0, 0)   // left, top
);
// }}}


#if defined(SIMPLE) || defined(BACKGROUND) || defined(SPECIAL)
#define NEEDS_BACKROUND
#endif

#if defined(SIMPLE) || defined(FOREGROUND)
#define NEEDS_FOREGROUND
#endif

#ifdef NEEDS_BACKROUND
out vec3 background;
#if defined(TRANSPARENT) || defined(SPECIAL)
out float bg_alpha;
#endif
#endif

#ifdef NEEDS_FOREGROUND
uniform float inactive_text_alpha;
uniform float dim_opacity;
out vec3 sprite_pos;
out vec3 underline_pos;
out vec3 cursor_pos;
out vec4 cursor_color_vec;
out vec3 strike_pos;
out vec3 foreground;
out vec3 decoration_fg;
out float colored_sprite;
out float effective_text_alpha;
#endif


// Utility functions {{{
const uint BYTE_MASK = uint(0xFF);
const uint Z_MASK = uint(0xFFF);
const uint COLOR_MASK = uint(0x4000);
const uint ZERO = uint(0);
const uint ONE = uint(1);
const uint TWO = uint(2);
const uint THREE = uint(3);
const uint FOUR = uint(4);

vec3 color_to_vec(uint c) {
    uint r, g, b;
    r = (c >> 16) & BYTE_MASK;
    g = (c >> 8) & BYTE_MASK;
    b = c & BYTE_MASK;
    return vec3(float(r) / 255.0, float(g) / 255.0, float(b) / 255.0);
}

uint resolve_color(uint c, uint defval) {
    // Convert a cell color to an actual color based on the color table
    int t = int(c & BYTE_MASK);
    uint r;
    switch(t) {
        case 1:
            r = color_table[(c >> 8) & BYTE_MASK];
            break;
        case 2:
            r = c >> 8;
            break;
        default:
            r = defval;
    }
    return r;
}

vec3 to_color(uint c, uint defval) {
    return color_to_vec(resolve_color(c, defval));
}

vec3 to_sprite_pos(uvec2 pos, uint x, uint y, uint z) {
    vec2 s_xpos = vec2(x, float(x) + 1.0) * sprite_dx;
    vec2 s_ypos = vec2(y, float(y) + 1.0) * sprite_dy;
    return vec3(s_xpos[pos.x], s_ypos[pos.y], z);
}

vec3 choose_color(float q, vec3 a, vec3 b) {
    return mix(b, a, q);
}

float are_integers_equal(float a, float b) { // return 1 iff equal otherwise 0
    float delta = abs(a - b);  // delta can be 0, 1 or larger
    return step(delta, 0.5); // 0 if 0.5 < delta else 1
}

float is_cursor(uint xi, uint y) {
    float x = float(xi);
    float y_equal = are_integers_equal(float(y), cursor_y);
    float x1_equal = are_integers_equal(x, cursor_x);
    float x2_equal = are_integers_equal(x, cursor_w);
    float x_equal = step(0.5, x1_equal + x2_equal);
    return step(2.0, x_equal + y_equal);
}
// }}}


void main() {

    // set cell vertex position  {{{
    uint instance_id = uint(gl_InstanceID);
    /* The current cell being rendered */
    uint r = instance_id / xnum;
    uint c = instance_id - r * xnum;

    /* The position of this vertex, at a corner of the cell  */
    float left = xstart + c * dx;
    float top = ystart - r * dy;
    vec2 xpos = vec2(left, left + dx);
    vec2 ypos = vec2(top, top - dy);
    uvec2 pos = cell_pos_map[gl_VertexID];
    gl_Position = vec4(xpos[pos.x], ypos[pos.y], 0, 1);

    // }}}

    // set cell color indices {{{
    uvec2 default_colors = uvec2(default_fg, default_bg);
    uint text_attrs = sprite_coords[3];
    uint is_inverted = ((text_attrs >> REVERSE_SHIFT) & ONE) + inverted;
    int fg_index = fg_index_map[is_inverted];
    int bg_index = 1 - fg_index;
    float cell_has_cursor = is_cursor(c, r);
    float is_block_cursor = step(float(cursor_fg_sprite_idx), 0.5);
    float cell_has_block_cursor = cell_has_cursor * is_block_cursor;
    vec3 bg = to_color(colors[bg_index], default_colors[bg_index]);
    // }}}

    // Foreground {{{
#ifdef NEEDS_FOREGROUND

    // The character sprite being rendered
    sprite_pos = to_sprite_pos(pos, sprite_coords.x, sprite_coords.y, sprite_coords.z & Z_MASK);
    colored_sprite = float((sprite_coords.z & COLOR_MASK) >> 14);

    // Foreground
    uint resolved_fg = resolve_color(colors[fg_index], default_colors[fg_index]);
    foreground = color_to_vec(resolved_fg);
    float has_dim = float((text_attrs >> DIM_SHIFT) & ONE);
    effective_text_alpha = inactive_text_alpha * mix(1.0, dim_opacity, has_dim);
    // Selection
    foreground = choose_color(float(is_selected & ONE), color_to_vec(highlight_fg), foreground);
    // Underline and strike through (rendered via sprites)
    float in_url = float((is_selected & TWO) >> 1);
    decoration_fg = choose_color(in_url, color_to_vec(url_color), to_color(colors[2], resolved_fg));
    underline_pos = choose_color(in_url, to_sprite_pos(pos, url_style, ZERO, ZERO), to_sprite_pos(pos, (text_attrs >> DECORATION_SHIFT) & THREE, ZERO, ZERO));
    strike_pos = to_sprite_pos(pos, ((text_attrs >> STRIKE_SHIFT) & ONE) * FOUR, ZERO, ZERO);

    // Cursor
    cursor_color_vec = vec4(color_to_vec(cursor_color), 1.0);
    foreground = choose_color(cell_has_block_cursor, CURSOR_TEXT_COLOR, foreground);
    decoration_fg = choose_color(cell_has_block_cursor, CURSOR_TEXT_COLOR, decoration_fg);
    cursor_pos = to_sprite_pos(pos, cursor_fg_sprite_idx * uint(cell_has_cursor), ZERO, ZERO);
#endif
    // }}}

    // Background {{{
#ifdef NEEDS_BACKROUND

#if defined(BACKGROUND)
    background = bg;
#endif

#if defined(TRANSPARENT) && !defined(SPECIAL)
    // If the background color is default, set its opacity to background_opacity, otherwise it should be opaque
    bg_alpha = step(0.5, float(colors[bg_index] & BYTE_MASK));
    // Cursor must not be affected by background_opacity
    bg_alpha = mix(bg_alpha, 1.0, cell_has_block_cursor);
    bg_alpha = bg_alpha + (1.0f - bg_alpha) * background_opacity;
#endif

#if defined(SPECIAL) || defined(SIMPLE)
    // Selection and cursor
    bg = choose_color(float(is_selected & ONE), color_to_vec(highlight_bg), bg);
    background = choose_color(cell_has_block_cursor, color_to_vec(cursor_color), bg);
#ifdef SPECIAL
    // bg_alpha should be 1 if cursor/selection otherwise 0
    bg_alpha = mix(0.0, 1.0, step(0.5, float(is_selected & ONE) + cell_has_block_cursor));
#endif
#endif

#endif
    // }}}

}
