热浪扭曲效果

   热浪扭曲•         每个人都对自然界中的这种大气效果很熟悉•         光线在穿过不同密度的介质时会弯曲 热微光•         热空气密度比冷空气小•         密度影响介质的折射率•         热空气上升的同时会被冷空气替代, 这会改变光射入眼睛的路线 •         渲染场景到RGBA离屏缓存(可渲染的纹理)•         颜色写入RGB值•         扭曲度写入Alpha通道•         绘制全屏长方形到后备缓冲区•         对离屏缓冲采样以获得扭曲度•         用扰动贴图来确定扰动向量, 用扭曲度放缩后偏移原始纹理坐标•         基于扰动纹理坐标的可增长泊松分布(根据扭曲度来进行偏移) 扭曲度•         逐像素判断当前像素被扭曲的程度•         当光线穿过更多的气体时, 折射程度也相应增加•         扭曲随场景深度增加–    开始时把渲染目标的Alpha通道清为1.0,表示最大深度–    Pixel shader把每个像素的深度写入alpha通道 •         深度提供了一个很好的全局扭曲方案, 但是你的美工们希望局部控制•         热浪几何体可以用来定义扭曲范围, 如热空气出口和喷气发动机尾•         热浪纹理可以使热浪几何本上的扭曲动起来 热度几何体 & 热度纹理•         像素扭曲度来源来热度纹理•         扭曲度被深度放大•         用高度进一步放大 (纹理坐标) 并且 N.V 来避免生硬的边缘•         扭曲度被写入Alpha通道 全屏矩形 •         全屏矩形用离屏缓存(可渲染的纹理)来绘制并且用扰动贴图作为纹理 扰动贴图•         一个2D向量储存在红色和绿色通道内•         在全屏矩形两个方向上卷动贴图并采样两次•         平均两次采样并把值变换到 [-1.0, 1.0] 的范围内•         用扭曲度放缩向量•         结果就是扭曲向量扭曲向量•         扭曲向量用于偏移原始纹理坐标•         向量的大小取决于扭曲度•         这个新的扰动纹理用于读入离屏缓存 可增长泊松分布•         模糊中心在扰动纹理坐标的中间•         偏移基于扭曲度 扭曲 Shader

float4 main (PsInput i) :COLOR{   // fetch from perturbation map with scrolling texture coords   float3 vPerturb0 =tex2D (tPerturbationMap, i.texCoord1);   float3 vPerturb1 =tex2D (tPerturbationMap, i.texCoord2);               // scale and bias: (color - 0.5f)*2.0f   vPerturb0 = SiConvertColorToVector(vPerturb0);   vPerturb1 = SiConvertColorToVector(vPerturb1);    // average perturbation vectors   float2 offset = (vPerturb0.xy + vPerturb1.xy) * 0.5f;    // get distortion weight from renderable texture (stored in alpha)   float4 cDistWeight =tex2D (tRBFullRes, i.texCoord0);    // square distortion weight   cDistWeight.a *= cDistWeight.a;    // compute distorted texture coords   offset.xy = ((offset.xy * cDistWeight.a) * fPerturbScale) + i.texCoord0;    // fetch the distorted color   float4 o;   o.rgb = SiPoissonDisc13RGB(tRBFullRes, offset, 1.0f/screenRes.xy, cDistWeight.a);   o.a = 1.0f;   return o;}

 可增长泊松分布 Shader

float3 SiGrowablePoissonDisc13FilterRGB(sampler tSource,float2 texCoord,float2 pixelSize,float discRadius){   float3 cOut;   float2 poisson[12] = {float2(-0.326212f, -0.40581f),                         float2(-0.840144f, -0.07358f),                         float2(-0.695914f, 0.457137f),                         float2(-0.203345f, 0.620716f),                         float2(0.96234f, -0.194983f),                         float2(0.473434f, -0.480026f),                         float2(0.519456f, 0.767022f),                         float2(0.185461f, -0.893124f),                         float2(0.507431f, 0.064425f),                         float2(0.89642f, 0.412458f),                         float2(-0.32194f, -0.932615f),                         float2(-0.791559f, -0.59771f)};   // Center tap   cOut = tex2D (tSource, texCoord);   for (int tap = 0; tap <12; tap++)   {      float2 coord = texCoord.xy + (pixelSize * poisson[tap] * discRadius);       // Sample pixel      cOut += tex2D (tSource, coord);   }   return (cOut / 13.0f);}