Simulate and light the smoke on the GPU and make rain and snow of particles

shaders/particle_soft.glsl

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+// soft particles (opengl46_gpu_particles): a particle fades where it nears what is behind it, instead of being cut by it.
+// the resolved depth of the scene drawn so far (gl::SCENE_DEPTH_TEX), reversed with the far plane at infinity: the distance
+// along the axis of the view is the near plane over the depth, and the sky, which writes no depth, stays at 0
+
+#ifndef PARTICLE_SOFT_GLSL
+#define PARTICLE_SOFT_GLSL
+
+layout(binding = SCENE_DEPTH_TEX) uniform sampler2D particle_scene_depth;
+
+// share of the particle left at the fragment, 0-1: Range (metres) is how far in front of the scene it fades out over, 0 for none.
+// Fragdistance: of the fragment along the axis of the view
+float particle_soft_fade(float range, float fragdistance)
+{
+	if (range <= 0.0)
+		return 1.0;
+	float depth = texelFetch(particle_scene_depth, ivec2(gl_FragCoord.xy), 0).r;
+	if (depth <= 0.0)
+		return 1.0;
+	float scene = projection[3][2] / depth;
+	float share = clamp((scene - fragdistance) / range, 0.0, 1.0);
+	return share * share * (3.0 - 2.0 * share);
+}
+
+#endif