#version 450

// Terminal cell renderer. The CPU uploads one instance per visible cell; this
// shader expands each instance into a two-triangle quad with gl_VertexIndex.
// The fragment shader mixes fg/bg by the atlas's alpha (a glyph mask in the R
// channel), so background fills and glyph foregrounds draw in a single pass.

layout(location = 0) in vec4 a_rect; // x0, y0, x1, y1
layout(location = 1) in vec4 a_uv_rect; // u0, v0, u1, v1
layout(location = 2) in vec3 a_fg;
layout(location = 3) in vec3 a_bg;
// Final and presented panel rectangles in NDC. The CPU still uploads logical
// final cells; this shader is the only place transition geometry is applied.
layout(location = 4) in vec4 a_panel_rect;
layout(location = 5) in vec4 a_present_rect;
// effect id, eased-progress float bits, pane serial, local row/column packed
// into one uint. The FIVE high effect bits are flags — the frozen-old cell
// layer, a see-through cell background, an opaque block-cursor fill, a soft
// shadow (decor.frag.glsl) or dotted page ground (ui.frag.glsl), and a
// checker (decor) or a file name's shadow (ui) — so the id is what is left
// below them; integer transport preserves the exact
// cross-backend hash.
layout(location = 6) in uvec4 a_effect;
// A clip rectangle in target pixels (x0, y0, x1, y1): the fragment shader
// drops what lies outside it. x1 < x0 is none. A vertical transition clips
// its pane's instances to the box the pane is growing into.
layout(location = 7) in vec4 a_clip;

layout(location = 0) out vec2 v_uv;
layout(location = 1) out vec3 v_fg;
layout(location = 2) out vec3 v_bg;
layout(location = 3) out vec2 v_cell_uv;
layout(location = 4) flat out uvec4 v_effect;
layout(location = 5) flat out vec4 v_clip;

void main() {
    vec2 pos;
    vec2 uv;
    int corner = gl_VertexIndex % 6;
    if (corner == 0) {
        pos = vec2(a_rect.x, a_rect.y);
        uv = vec2(a_uv_rect.x, a_uv_rect.y);
        v_cell_uv = vec2(0.0, 0.0);
    } else if (corner == 1) {
        pos = vec2(a_rect.z, a_rect.y);
        uv = vec2(a_uv_rect.z, a_uv_rect.y);
        v_cell_uv = vec2(1.0, 0.0);
    } else if (corner == 2) {
        pos = vec2(a_rect.z, a_rect.w);
        uv = vec2(a_uv_rect.z, a_uv_rect.w);
        v_cell_uv = vec2(1.0, 1.0);
    } else if (corner == 3) {
        pos = vec2(a_rect.x, a_rect.y);
        uv = vec2(a_uv_rect.x, a_uv_rect.y);
        v_cell_uv = vec2(0.0, 0.0);
    } else if (corner == 4) {
        pos = vec2(a_rect.z, a_rect.w);
        uv = vec2(a_uv_rect.z, a_uv_rect.w);
        v_cell_uv = vec2(1.0, 1.0);
    } else {
        pos = vec2(a_rect.x, a_rect.w);
        uv = vec2(a_uv_rect.x, a_uv_rect.w);
        v_cell_uv = vec2(0.0, 1.0);
    }

    uint effect = a_effect.x & 0x07ffffffu;
    if (effect == 1u || effect == 2u || effect == 5u) {
        // NDC y points up, so a top-left/bottom-right box has a NEGATIVE y
        // delta. Preserve that sign or every local y is mirrored/outside.
        vec2 panel_size = a_panel_rect.zw - a_panel_rect.xy;
        panel_size.x = abs(panel_size.x) < 0.000001 ? 0.000001 : panel_size.x;
        panel_size.y = abs(panel_size.y) < 0.000001 ? -0.000001 : panel_size.y;
        vec2 within = (pos - a_panel_rect.xy) / panel_size;
        pos = mix(a_present_rect.xy, a_present_rect.zw, within);
    }
    v_uv = uv;
    v_fg = a_fg;
    v_bg = a_bg;
    v_effect = a_effect;
    v_clip = a_clip;
    gl_Position = vec4(pos, 0.0, 1.0);
}