開始感受到電腦繪圖算法的迷人之處，可惜再沒有人和我分享這份喜悅
。
讓我嘗試簡單地解釋它的原理吧。
螢幕中的每一像素都會和它周圍的 N 個像素作比較，比較時有兩個因數需要考慮
- 兩像素於三圍空間中的位置；深度較淺的像素會遮蔽較深的像素，而遮蔽的程度就取決於距離。
- 兩像素的法線內積 (Dot product)；面向面的像素會比面向同一方向的像素較接觸不到外來的光線。
uniform sampler2DRect texColor; // Color texture
uniform sampler2DRect texDepth; // Depth texture
uniform sampler2DRect texNormal;// Normal texture
uniform vec2 camerarange = vec2(1.0, 500);
varying vec2 texCoord;
const float aoCap = 1.0;
float aoMultiplier = 1000.0;
float pw = 1.0; // Use (1.0 / screensize.x) for GL_TEXTURE2D
float ph = 1.0;
float readDepth(in vec2 coord)
{
float nearZ = camerarange.x;
float farZ = camerarange.y;
float posZ = texture2DRect(texDepth, coord).x;
return (2.0 * nearZ) / (nearZ + farZ - posZ * (farZ - nearZ));
}
vec3 readNormal(in vec2 coord)
{
return normalize(2 * (texture2DRect(texNormal, coord).xyz - 1));
}
float compareDepths(in float depth1, in float depth2)
{
float depthDiff = depth1 - depth2;
const float aorange = 10.0; // Units in space the AO effect extends to (this gets divided by the camera far range)
float diff = clamp(1.0 - depthDiff * (camerarange.y - camerarange.x) / aorange, 0.0, 1.0);
return min(aoCap, max(0.0, depthDiff) * aoMultiplier) * diff;
}
float calAO(float depth, vec3 normal, float dw, float dh)
{
vec2 coord = vec2(texCoord.x + dw, texCoord.y + dh);
float angleFactor = 1 - dot(normal, readNormal(coord));
if(length(normal) == 0)
angleFactor = 0;
return angleFactor * compareDepths(depth, readDepth(coord));
}
void main(void)
{
float depth = readDepth(texCoord);
float ao = 0.0;
vec3 normal = readNormal(texCoord);
for(int i=0; i<8; ++i) {
ao += calAO(depth, normal, pw, ph);
ao += calAO(depth, normal, pw, -ph);
ao += calAO(depth, normal, -pw, ph);
ao += calAO(depth, normal, -pw, -ph);
pw *= 1.4;
ph *= 1.4;
aoMultiplier /= 1.5;
}
ao *= 2.0;
gl_FragColor = vec4(1.0 - ao) * texture2DRect(texColor, texCoord);
}
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