I have a deferred rendering system, and I am testing at full 1920x1080 and noticing that a particular fragment shader is causing significant slowdown (they all seem oddly slow, but this one seems the most significant). My shader is based on the OGL-Dev tutorials for deferred rendering.
The purpose of this shader is to calculate the added light within a light's area of effect. There are 3 large point lights in my scene, that cover everything in view. So essentially this shader is executing 3 times for every pixel on the screen.
I measured the difference in frame time between running this shader, and then replacing the shader's main function with a simple "FragColor = vec4(1,0,0,1); //red". The total difference in time (for my engine to render an entire frame) is 4-5 milliseconds. If I'm shooting for 60 fps, that's already 25+% of my full frame render time, which seems kind of crazy (I removed shadow calculation and blur before taking these measurements).
Here is my shader:
#version 420
layout (location = 0) out vec4 FragColor;
struct BaseLight
{
vec3 Color;
float AmbientIntensity;
float DiffuseIntensity;
};
struct Attenuation
{
float Constant;
float Linear;
float Exp;
};
struct PointLight
{
BaseLight Base;
vec3 Position;
Attenuation Atten;
};
uniform sampler2D gPositionMap;
uniform sampler2D gColorMap;
uniform sampler2D gNormalMap;
uniform sampler2D gShadowMap;
uniform PointLight gPointLight;
uniform vec3 gEyeWorldPos;
uniform float gMatSpecularIntensity;
uniform float gSpecularPower;
uniform int gLightType;
uniform vec2 gScreenSize;
uniform mat4 gWVP;
uniform mat4 gVP;
uniform mat4 gView;
vec4 CalcLightInternal(BaseLight Light,
vec3 LightDirection,
vec3 WorldPos,
vec3 Normal, float shadowFactor )
{
vec4 AmbientColor = vec4(Light.Color, 1.0f) * Light.AmbientIntensity;
float DiffuseFactor = dot(Normal, -LightDirection);
float shadowFactorOrig = shadowFactor;
vec4 DiffuseColor = vec4(0, 0, 0, 0);
vec4 SpecularColor = vec4(0, 0, 0, 0);
if (DiffuseFactor > 0) {
DiffuseColor = vec4(0,1,0,1);
DiffuseColor = vec4(Light.Color, 1.0f) * DiffuseFactor ;
vec3 VertexToEye = normalize(gEyeWorldPos - WorldPos);
vec3 LightReflect = normalize(reflect(LightDirection, Normal));
float SpecularFactor = dot(VertexToEye, LightReflect);
SpecularFactor = pow(SpecularFactor, gSpecularPower);
if (SpecularFactor > 0) {
SpecularColor = vec4(Light.Color, 1.0f) * gMatSpecularIntensity * SpecularFactor;
}
}
return (AmbientColor + shadowFactor*(DiffuseColor+SpecularColor));
}
vec4 CalcPointLight(vec3 WorldPos, vec3 Normal)
{
vec3 LightDirection = WorldPos - gPointLight.Position;
float Distance = length(LightDirection);
LightDirection = normalize(LightDirection);
vec4 Color = CalcLightInternal(gPointLight.Base, LightDirection, WorldPos, Normal,1.0f);
float Attenuation = gPointLight.Atten.Constant +
gPointLight.Atten.Linear * Distance +
gPointLight.Atten.Exp * Distance * Distance;
Attenuation = min(1.0, Attenuation);
return Color / Attenuation;
}
vec2 CalcTexCoord()
{
return gl_FragCoord.xy / gScreenSize;
}
void main()
{
vec2 TexCoord = CalcTexCoord();
vec3 WorldPos = texture(gPositionMap, TexCoord).xyz;
vec3 Color = texture(gColorMap, TexCoord).xyz;
vec3 Normal = texture(gNormalMap, TexCoord).xyz;
Normal = normalize(Normal);
FragColor = CalcPointLight(WorldPos, Normal);
} I am on a fairly fast HP machine with plenty of memory and a NVIDIA Quadro K1100M graphics card. Also, I already checked the VSync to make sure my render times are not forcing my render times to be multiples of 16ms.
This shader does not contain an inordinate amount of looping or branching. It is executing about 3 times per pixel. Should this really be adding 4-5 milliseconds to my render times?
Any ideas for what could be causing this would be much appreciated.
