(Vulkan) Add pipeline simple snow

gfx/drivers/vulkan_shaders/pipeline_snow_simple.frag

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+#version 310 es
+
+layout(location = 0) in vec3 VertexCoord;
+
+layout(std140, set = 0, binding = 0) uniform UBO
+{
+   float time;
+} constants;
+
+void main()
+{
+   gl_Position = MVPMatrix * vec4(VertexCoord, 0.0, 1.0);
+}

gfx/drivers/vulkan_shaders/pipeline_snow_simple.vert

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+#version 310 es
+precision highp float;
+
+layout(std140, set = 0, binding = 0) uniform UBO
+{
+   float time;
+} constants;
+
+layout(location = 0) out vec4 FragColor;
+
+	vec2 res = vec2(1920*3, 1080*3);
+
+	// High quality = larger patterns
+	// quality * 84 is the number of seconds in a loop
+	float quality = 8.0;
+	
+	float Cellular2D(vec2 P) {
+		//  https://github.com/BrianSharpe/Wombat/blob/master/Cellular2D.glsl
+		vec2 Pi = floor(P);
+		vec2 Pf = P - Pi;
+		vec2 Pt = vec2( Pi.x, Pi.y + 1.0 );
+		Pt = Pt - floor(Pt * ( 1.0 / 71.0 )) * 71.0;
+		Pt += vec2( 26.0, 161.0 ).xy;
+		Pt *= Pt;
+		Pt = Pt.xy * Pt.yx;
+		float hash_x = fract( Pt * ( 1.0 / 951.135664 ) ).x * 2.0 - 1.0;
+		float hash_y = fract( Pt * ( 1.0 / 642.949883 ) ).y * 2.0 - 1.0;
+		const float JITTER_WINDOW = 0.25;
+		hash_x = ( ( hash_x * hash_x * hash_x ) - sign( hash_x ) ) * JITTER_WINDOW;
+		hash_y = ( ( hash_y * hash_y * hash_y ) - sign( hash_y ) ) * JITTER_WINDOW;
+		vec2 dd = vec2(Pf.x - hash_x, Pf.y - hash_y);
+		float d = dd.x * dd.x + dd.y * dd.y;
+		return d * ( 1.0 / 1.125 );
+	}
+	
+	float snow(vec2 pos, float time, float scale) {
+		// add wobble
+		pos.x += cos(pos.y*4.0 + time*3.14159*2.0 + 1.0/scale)/(8.0/scale);
+		// add gravity
+		pos += time*scale*vec2(-0.5, 1.0);
+		return max(
+			1.0 - Cellular2D(mod(pos/scale, scale*quality)*16.0)*1024.0,
+			0.0
+		) * (scale*0.5 + 0.5);
+	}
+
+void main()
+{
+		float winscale = max(res.x, res.y);
+		float tim = mod(constants.time/800.0, 84.0*quality);
+		vec2 pos = gl_FragCoord.xy/winscale;
+		float a = 0.0;
+		// Each of these is a layer of snow
+		// Remove some for better performance
+		// Changing the scale (3rd value) will mess with the looping
+		a += snow(pos, tim, 1.0);
+		a += snow(pos, tim, 0.7);
+		a += snow(pos, tim, 0.6);
+		a += snow(pos, tim, 0.5);
+		a += snow(pos, tim, 0.4);
+		a += snow(pos, tim, 0.3);
+		a += snow(pos, tim, 0.25);
+		a += snow(pos, tim, 0.125);
+		a = a * min(pos.y*4.0, 1.0);
+		FragColor = vec4(1.0, 1.0, 1.0, a);
+}