#version 450

layout(location = 0) in vec3 in_position;
layout(location = 1) in vec3 in_color;

layout(location = 0) out vec3 frag_color;

layout(push_constant) uniform PushConstants {
    mat4 mvp;
    // xyz is the chunk's world offset; w is the debug-tint weight, 0.0 for normal rendering and 1.0 for a debug raster pass.
    vec4 chunk_offset;
} push_constants;

// Colour applied to debug raster passes, chosen to contrast with terrain and to remain legible when overlaid on filled geometry.
const vec3 DEBUG_COLOR = vec3(1.0, 0.0, 1.0);

// Size, in pixels, of the points emitted under VK_POLYGON_MODE_POINT. Sizes above 1.0 require the largePoints device feature.
const float DEBUG_POINT_SIZE = 5.0;

void main() {
    // The chunk-local vertex is shifted into world space by the per-chunk offset before projection.
    vec3 world_position = in_position + push_constants.chunk_offset.xyz;
    gl_Position = push_constants.mvp * vec4(world_position, 1.0);

    // Point size is consulted whenever the polygon mode is POINT; leaving it unwritten renders points of undefined size. It is ignored by the FILL and LINE pipelines, so it is written unconditionally.
    gl_PointSize = DEBUG_POINT_SIZE;

    float debug_tint = push_constants.chunk_offset.w;
    frag_color = mix(in_color, DEBUG_COLOR, debug_tint);
}