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Member Since 06 Nov 2012
Offline Last Active Nov 15 2012 05:41 PM

Topics I've Started

Deferred shading - light accumulation issue

07 November 2012 - 01:50 PM

I'm working on deferred shading and all has gone well until it comes time to render multiple lights. The first shader pass renders my scene to a G-buffer with color (albedo), position, normal, and material (specular, etc) data written to color attachments. The next shader passes create and blur a SSAO texture from the normal data and a randomizer, and it looks nice. Then I do the final lighting pass. I start experimenting by rendering out a sphere to represent a large point light (see fig. 1) and it looks mostly like what I would expect. So far so good.

My goal is to draw a ton of lights in my scene. When I add a second light, it occludes the first (see fig. 2). I've tried using glAccum() to no avail. When I render a second light which overlaps the first in screen space (see fig. 3 and fig. 4), that pixel is overwritten. I'm having trouble understanding how to create and display a light accumulation buffer in a single shader pass. I could ping-pong FBOs between lights, but that seems like it would be really slow, and has not been suggested in any material I've read.

My vertex shader (see fig. 5) and fragment shader (see fig. 6) in my lighting pass are below.

Fig 1. One light
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Fig 2. Two lights, occluding instead of accumulating
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Fig 3. Spheres representing lights
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Fig 4. Zoom out of fig. 3
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Fig. 5 Lighting pass vertex shader
varying vec4  lightPosition;

void main( void )
	 lightPosition = gl_ModelViewProjectionMatrix * gl_Vertex;
	 gl_Position  = lightPosition;

Fig. 6 Lighting pass fragment shader
uniform vec3 eyePoint;		 // Camera eye point
uniform vec4 lightAmbient;	 // Light ambient color
uniform vec3 lightCenter;	 // Center of light shape
uniform vec4 lightDiffuse;	 // Light diffuse color
uniform float lightRadius;	 // Size of light
uniform vec4 lightSpecular;	 // Light specular color
uniform vec2 pixel;              // To convert pixel coords to [0,0]-[1,1]
uniform sampler2D texAlbedo;	 // Color data
uniform sampler2D texMaterial;   // R=spec level, G=spec power, B=emissive
uniform sampler2D texNormal;	 // Normal-depth map
uniform sampler2D texPosition;   // Position data
uniform sampler2D texSsao;	 // SSAO

varying vec4  lightPosition;	 // Position of current vertex in light

void main()

	 // Get screen space coordinate
	 vec2 uv         = gl_FragCoord.xy * pixel;

	 // Sample G-buffer
	 vec4 albedo     = texture2D( texAlbedo,   uv );
	 vec4 material   = texture2D( texMaterial, uv );
	 vec4 normal     = texture2D( texNormal,   uv );
	 vec4 position   = texture2D( texPosition, uv );
	 vec4 ssao       = texture2D( texSsao,     uv );

	 // Calculate reflection
	 vec3 eye        = normalize( -eyePoint );
	 vec3 light      = normalize( lightCenter.xyz - position.xyz );  
	 vec3 reflection = normalize( -reflect( light, normal.xyz ) );

	 // Calculate light values
	 vec4 ambient    = lightAmbient;
	 vec4 diffuse    = clamp( lightDiffuse * max( dot( normal.xyz, light ), 0.0 ), 0.0, 1.0 );
	 vec4 specular   = clamp( material.r * lightSpecular * pow( max( dot( reflection, eye ), 0.0 ), material.g ), 0.0, 1.0 );
	 vec4 emissive   = material.b;

	 // Combine color and light values
	 vec4 color      = albedo;
	 color           += ambient + diffuse + specular + emissive;

	 // Apply light falloff
	 float falloff    = 1.0 - distance( lightPosition, position ) / lightRadius;
	 color           *= falloff;

	 // Apply SSAO
	 color           -= vec4( 1.0 ) * ( 1.0 - ssao.r );

	 // Set final color
	 gl_FragColor    = color;

Deferred shading - light accumulation issue

07 November 2012 - 12:39 PM

Sorry, I'm new here. Posted in wrong forum, but can't delete. Post moved here: