#version 430 core
#extension GL_ARB_bindless_texture : require
in vec2 vUv;
in vec4 vColor;
out vec4 FragColor;

// Campaign V slice V6d: the retained UI samples the device's global texture
// table instead of whatever happened to be bound to texture unit 0. The old
// `uniform sampler2D uTex` plus `uniform int uUseTexture` pair could not exist
// under Vulkan — there is no default uniform block, and an opaque sampler
// cannot be a push constant — so both are expressed with the pinned block's two
// texture-table slots. There is no third field and none was needed: which slots
// are ASSIGNED is itself the mode.
//
//   uTextureIndexB assigned -> single-channel coverage source (a font atlas):
//                              red is the glyph's alpha, and the colour's RGB
//                              is NOT multiplied by it.
//   uTextureIndexA assigned -> RGBA colour source (dat chrome, icons, sprites),
//                              modulated by the vertex colour/tint.
//   neither assigned        -> a flat quad in the vertex colour. Untextured
//                              rects and DrawFill take this path; the old
//                              shader's uUseTexture==0 branch is unchanged.
//
// Exactly one of the two is ever assigned at a time, so the branch is uniform
// across a draw.
uniform uint uTextureIndexA;
uniform uint uTextureIndexB;

// GpuTextureSlot.Unassigned. It is a loud sentinel precisely so it can be
// tested for rather than silently resolving to slot 0 — the failure mode that
// produced the magenta 1x1 UI placeholder. Both branches below are guarded, so
// it never reaches a sampler.
const uint kUnassignedTextureSlot = 0xFFFFFFFFu;

void main() {
    if (uTextureIndexB != kUnassignedTextureSlot) {
        // Font atlas is a single-channel R8 texture; red = coverage alpha.
        float coverage = ACDREAM_SAMPLE_2D(uTextureIndexB, vUv).r;
        FragColor = vec4(vColor.rgb, vColor.a * coverage);
    } else if (uTextureIndexA != kUnassignedTextureSlot) {
        // RGBA dat sprite (decoded to RGBA8); modulate by tint/alpha.
        FragColor = ACDREAM_SAMPLE_2D(uTextureIndexA, vUv) * vColor;
    } else {
        FragColor = vColor;
    }
    if (FragColor.a < 0.005) discard;
}