陰影映射

完成了紋理投影後，製作基本陰影映射就如吃生菜一樣容易。

// Pixel shader

varying vec3 normal, lightDir, halfVector;
varying vec2 colorCoord;
varying vec4 shadowCoord;
uniform sampler2D colorTex;
uniform sampler2DShadow shadowTex;

// Light intensity inside shadow
const float shadowIntensity = 0.5;

// Should be supplied as uniform
const float shadowMapPixelScale = 1.0 / float(2048);
const int pcfSize = 1; // The pcf filtering size, 0 -> 1x1 (no filtering), 1 -> 3x3 etc

void main(void)
{
 vec4 diffuse = gl_FrontLightProduct[0].diffuse;
 vec4 specular = gl_FrontLightProduct[0].specular;
 vec4 ambient = gl_FrontLightProduct[0].ambient;
 vec3 n = normalize(normal);
 float NdotL = max(dot(n, lightDir), 0.0);

 diffuse *= NdotL;
 vec3 halfV = normalize(halfVector);
 float NdotHV = max(dot(n, halfV), 0.0);
 specular *= pow(NdotHV, gl_FrontMaterial.shininess);

 // Get the shadow value, let the hardware perform perspective divide,
 // depth comparison and 2x2 pcf if supported.
 // float shadowValue = shadow2DProj(shadowTex, shadowCoord).r;

 // Perform PCF filtering
 float shadowValue = 0.0;
 for(int i=-pcfSize; i<=pcfSize; ++i) for(int j=-pcfSize; j<=pcfSize; ++j)
 {
  vec4 offset = vec4(i * shadowMapPixelScale, j * shadowMapPixelScale, 0, 0);
  shadowValue += shadow2DProj(shadowTex, shadowCoord + offset).r;
 }
 shadowValue /= (2 * pcfSize + 1) * (2 * pcfSize + 1);

 float shadowSpecularFactor = shadowValue == 0 ? 0 : 1;
 float shadowDiffuseFactor = min(1.0, shadowIntensity + shadowValue);

 gl_FragData[0] = shadowSpecularFactor * specular +
 (ambient + shadowDiffuseFactor * diffuse) * vec4(texture2D(colorTex, colorCoord).xyz, 1); 
}

當然，還有許多的陰影技術可以嘗試；我比較臨感興趣的有：

• Exponential Shadow Map
• Variance Shadow Map
• Trapezoidal Shadow Maps
• Parallel-Split Shadow Maps
  

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相關文章

• Code Sampler - Shadow mapping
  
• Paul's Project - Shadow mapping
• GDC08 Advanced Soft Shadow Mapping Techniques