GPUImageSphereRefractionFilter滤镜的Core Image Filte实现

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GPUImageSphereRefractionFilter滤镜的Core Image Filter实现

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/*
 * center:  中心坐标,取之范围0-1
 * radius: 取值范围0~0.5
 * aspectRatio : 输入图片的宽高比， 代码中已自动计算
 * refractiveIndex ： 反射率
 */

kernel vec4 coreImageKernel(sampler image, vec2 center, float radius, float aspectRatio, float refractiveIndex)
{
	//转换当前处理的坐标为贴图坐标，范围0.0~1.0
	vec2 pos =  destCoord();
	pos.x = pos.x / samplerSize(image).x;
	pos.y = pos.y / samplerSize(image).y;

	aspectRatio = samplerSize(image).y / samplerSize(image).x;
	vec4 color;
	highp vec2 textureCoordinateToUse = vec2(pos.x, (pos.y * aspectRatio + 0.5 - 0.5 * aspectRatio));
	highp float distanceFromCenter = distance(center, textureCoordinateToUse);
	lowp float checkForPresenceWithinSphere = step(distanceFromCenter, radius);

     distanceFromCenter = distanceFromCenter / radius;

     highp float normalizedDepth = radius * sqrt(1.0 - distanceFromCenter * distanceFromCenter);
     highp vec3 sphereNormal = normalize(vec3(textureCoordinateToUse - center, normalizedDepth));

     highp vec3 refractedVector = refract(vec3(0.0, 0.0, -1.0), sphereNormal, refractiveIndex);

	vec2 samplePos = (refractedVector.xy + 1.0) * 0.5;

	//还原贴图坐标为空间坐标
	samplePos.x  *= samplerSize(image).x;
	samplePos.y  *= samplerSize(image).y;
    color = sample(image, samplePos) * checkForPresenceWithinSphere;

	return color;

}