// MinecraftPT — RTWSM Backward Analysis
// Computes the importance map from the shadow map depth: which shadow map texels
// need more resolution (near-field geometry, steep normals).

#include "/Lib/Settings.glsl"
#include "/Lib/Utilities.glsl"
#include "/Lib/PathTracing/Voxelizer/VoxelProfile.glsl"

const ivec3 workGroups = ivec3(32, 16, 1);
layout (local_size_x = 32, local_size_y = 32) in;

layout (r32f) uniform writeonly image2D img_rtwImportance2D;

uniform sampler2D shadowcolor0;

void main(){
	ivec2 texel = ivec2(gl_GlobalInvocationID.xy);
	vec2 uv = (vec2(texel) + 0.5) / vec2(RTW_RESOLUTION, RTW_RESOLUTION_Y);

	// Sample shadow map depth (in the shadow region)
	vec2 shadowUv = vec2(uv.x * 0.5 + 0.5, uv.y * 0.5); // map to right region
	vec2 shadowTexel = shadowUv * shadowSize;

	vec4 shadowData = texelFetch(shadowcolor0, ivec2(shadowTexel), 0);

	float depth = shadowData.a;
	float importance = 0.0;

	if (depth < 1.0){
		// Depth-based importance: closer = more important
		float dist = 1.0 - depth;
		importance = pow(dist, 2.0) * RTW_BACKWARD_DIST_FACTOR;

		// Depth gradient importance (edges)
		float dLeft = texelFetch(shadowcolor0, ivec2(shadowTexel) + ivec2(-1, 0), 0).a;
		float dRight = texelFetch(shadowcolor0, ivec2(shadowTexel) + ivec2(1, 0), 0).a;
		float dUp = texelFetch(shadowcolor0, ivec2(shadowTexel) + ivec2(0, -1), 0).a;
		float dDown = texelFetch(shadowcolor0, ivec2(shadowTexel) + ivec2(0, 1), 0).a;

		float gradient = abs(dLeft - dRight) + abs(dUp - dDown);
		importance += gradient * 0.5 * RTW_BACKWARD_NORMAL_FACTOR;
	}

	imageStore(img_rtwImportance2D, texel, vec4(importance));
}