Rewrote the WebGPU bloom pass based on the classic Unreal solution of blurring and combining the levels of an image pyramid. Fixed the regl bloom pass to use the downscaled blurred mipmap levels to build the first pyramid.

shaders/wgsl/bloomCombine.wgsl

@@ -0,0 +1,31 @@
+[[block]] struct Config {
+	bloomStrength : f32;
+	pyramidHeight : f32;
+};
+
+[[group(0), binding(0)]] var<uniform> config : Config;
+[[group(0), binding(1)]] var linearSampler : sampler;
+[[group(0), binding(2)]] var tex : texture_2d<f32>;
+[[group(0), binding(3)]] var outputTex : texture_storage_2d<rgba8unorm, write>;
+
+struct ComputeInput {
+	[[builtin(global_invocation_id)]] id : vec3<u32>;
+};
+
+[[stage(compute), workgroup_size(32, 1, 1)]] fn computeMain(input : ComputeInput) {
+
+	var coord = vec2<i32>(input.id.xy);
+	var outputSize = textureDimensions(outputTex);
+
+	if (coord.x >= outputSize.x) {
+		return;
+	}
+
+	var uv = (vec2<f32>(coord) + 0.5) / vec2<f32>(outputSize);
+	var sum = vec4<f32>(0.0);
+	for (var i = 0.0; i < config.pyramidHeight; i = i + 1.0) {
+		sum = sum + (1.0 - i / config.pyramidHeight) * textureSampleLevel( tex, linearSampler, uv, i + 1.0 );
+	}
+
+	textureStore(outputTex, coord, sum * config.bloomStrength);
+}