add compute shader to auto calculate screen exposure, add SSBO impl

Editor/assets/shaders/SceneComposite.glsl

@@ -23,7 +23,14 @@ in vec2 v_TexCoord;
 
 uniform sampler2DMS u_Texture;
 
-uniform float u_Exposure;
+
+uniform bool u_EnableAutoExposure;
+uniform float u_ManualExposure;
+layout(std430, binding = 2) buffer Exposure
+{
+	float u_Exposure;
+};
+
 uniform int u_TextureSamples;
 
 uniform bool u_EnableBloom;
@@ -64,7 +71,10 @@ void main()
 		color += bloomColor;
 	}
 
-	color *= u_Exposure;
+	if(u_EnableAutoExposure)
+		color *= u_Exposure;
+	else
+		color *= u_ManualExposure;
 
 	// Reinhard tonemapping operator.
 	// see: "Photographic Tone Reproduction for Digital Images", eq. 4