DX9 Update中的HDRLighting Sample分析 (1)
这里着重分析整个渲染过程，至于HDR就不介绍了。(下面是流程图)
我们先来看看HDRLighting Sample里面比较重要的一些Texture:
PDIRECT3DTEXTURE9 m_pTexScene; // HDR render target containing the scene
//保持整个场景的FP Texture格式是D3DFMT_A16B16G16R16F这样保存的颜色值就可以突破0-1的限制
PDIRECT3DTEXTURE9 m_pTexSceneScaled; // Scaled copy of the HDR scene
//一个上面m_pTexScene的缩小到1/4的FP Texture格式和m_pTexScene一样，这个是我们后面的一些post-process的来源
PDIRECT3DTEXTURE9 m_pTexBrightPass; // Bright-pass filtered copy of the scene
//保存了m_pTexScene通过Bright-Pass Filter后的，只剩下了亮度高的部分。因为这个Texture不需要去做一些HDR相关的操作，
所以格式32bit贴图就行了。这个是后面我们做Bloom,Star的来源。
PDIRECT3DTEXTURE9 m_pTexAdaptedLuminanceCur; // The luminance that the user is currenly adapted to
//当前适合的亮度值，我们为了模拟出眼睛对于光的适应过程，采用的两个亮度值之一。格式是D3DFMT_R16F,大小是1x1
PDIRECT3DTEXTURE9 m_pTexAdaptedLuminanceLast; // The luminance that the user is currenly adapted to
//和上面的那个一样，我们通过交换这两个贴图来作出对于光的适应过程
PDIRECT3DTEXTURE9 m_pTexStarSource; // Star effect source texture
//做Star的来源，格式是D3DFMT_A8R8G8B8
PDIRECT3DTEXTURE9 m_pTexBloomSource; // Bloom effect source texture
//做Bloom的来源，格式是D3DFMT_A8R8G8B8
PDIRECT3DTEXTURE9 m_apTexBloom[NUM_BLOOM_TEXTURES]; // Blooming effect working textures
//Bloom效果用的系列贴图，格式是D3DFMT_A8R8G8B8，这里一共3张
PDIRECT3DTEXTURE9 m_apTexStar[NUM_STAR_TEXTURES]; // Star effect working textures
//Star效果用的系列贴图，格式是D3DFMT_A8R8G8B8，这里一共12张
PDIRECT3DTEXTURE9 m_apTexToneMap[NUM_TONEMAP_TEXTURES]; // Log average luminance samples
// from the HDR render target
//计算场景的亮度值用的系列贴图，格式是D3DFMT_R16F，在这里大小为1X1,4X4,16X16,64X64,一共4张
接下来就是整个的渲染过程 Render()
PDIRECT3DSURFACE9 pSurfLDR; // Low dynamic range surface for final output
PDIRECT3DSURFACE9 pSurfHDR; // High dynamic range surface to store
// intermediate floating point color values
// Setup HDR render target
m_pd3dDevice->GetRenderTarget(0, &pSurfLDR);
m_pTexScene->GetSurfaceLevel(0, &pSurfHDR);
// Clear the viewport
m_pd3dDevice->SetRenderTarget(0, pSurfHDR);
m_pd3dDevice->Clear(0L, NULL, D3DCLEAR_TARGET | D3DCLEAR_ZBUFFER, D3DCOLOR_RGBA(0, 0, 0, 0), 1.0f, 0L);
//这段代码保存了原始的RT,设置m_pTexScene为RT.
RenderScene();
//将Scene渲染到我们新的RT上，由于RT是FP的，我们能够保存超过0-1的数据
Scene_To_SceneScaled();
//将m_pTexScene渲染到m_pTexSceneScaled上，也就是缩小到1/4，这样的作用是在下面的处理能提高不少速度，我们看看这
个函数里面一些主要的操作:
HRESULT CMyD3DApplication::Scene_To_SceneScaled()
{
....
m_pEffect->SetTechnique("DownScale4x4");
//这里用到了DownScale4x4这段shader,我们仔细得看看这个shader
float4 DownScale4x4(in float2 vScreenPosition : TEXCOORD0) : COLOR
{
float4 sample = 0.0f;
for( int i=0; i < 16; i++ )
{
sample += tex2D( s0, vScreenPosition + g_avSampleOffsets[i] );
}
return sample / 16;
}
//这里就是按照g_avSampleOffsets的偏移值采样16个texel,然后计算均值。这个偏移数组的数据怎么样计算得出来的呢？
//我们注意到函数接下来的几行有这样两句
GetSampleOffsets_DownScale4x4( m_d3dsdBackBuffer.Width, m_d3dsdBackBuffer.Height, avSampleOffsets );
m_pEffect->SetValue("g_avSampleOffsets", avSampleOffsets, sizeof(avSampleOffsets));
//这两句就是计算出这个偏移数组并且设定到相应的位置,这里我们先不具体的看GetSampleOffsets_DownScale4x4函数，
通过这个函数得到的偏移数组是以原始采样点为中心的4X4的一个矩阵。
m_pd3dDevice->SetRenderTarget( 0, pSurfScaledScene );
m_pd3dDevice->SetTexture( 0, m_pTexScene );
m_pd3dDevice->SetSamplerState( 0, D3DSAMP_MINFILTER, D3DTEXF_POINT );
m_pd3dDevice->SetSamplerState( 0, D3DSAMP_ADDRESSU, D3DTADDRESS_CLAMP );
m_pd3dDevice->SetSamplerState( 0, D3DSAMP_ADDRESSV, D3DTADDRESS_CLAMP );
//这样我们就得到了1/4的版本pSurfScaledScene
}
//接下来就是求平均亮度的过程
if( m_bToneMap )
MeasureLuminance();
//我们仔细得看看这个函数里面执行的操作
HRESULT CMyD3DApplication::MeasureLuminance()
{
....
//首先这里是先计算了9个采样数据的偏移值
float tU, tV;
tU = 1.0f / (3.0f * desc.Width);
tV = 1.0f / (3.0f * desc.Height);
index=0;
for( x = -1; x <= 1; x++ )
{
for( y = -1; y <= 1; y++ )
{
avSampleOffsets[index].x = x * tU;
avSampleOffsets[index].y = y * tV;
index++;
}
}
//这9个形成3X3的矩阵
//接下来是设置相应的操作和数据
m_pEffect->SetTechnique("SampleAvgLum");
m_pEffect->SetValue("g_avSampleOffsets", avSampleOffsets, sizeof(avSampleOffsets));
m_pd3dDevice->SetRenderTarget(0, apSurfToneMap[dwCurTexture]);
m_pd3dDevice->SetTexture(0, m_pTexSceneScaled);
m_pd3dDevice->SetSamplerState( 0, D3DSAMP_MAGFILTER, D3DTEXF_LINEAR );
m_pd3dDevice->SetSamplerState( 0, D3DSAMP_MINFILTER, D3DTEXF_LINEAR );
m_pd3dDevice->SetSamplerState( 1, D3DSAMP_MAGFILTER, D3DTEXF_LINEAR );
m_pd3dDevice->SetSamplerState( 1, D3DSAMP_MINFILTER, D3DTEXF_LINEAR );
//在这里RT是m_apTexToneMap[3]，而shader操作则是一个取值，计算Log,计算均值得过程,下面是shader的代码
float4 SampleLumInitial(in float2 vScreenPosition : TEXCOORD0) : COLOR
{
float3 vSample = 0.0f;
float fLogLumSum = 0.0f;
for(int iSample = 0; iSample < 9; iSample++)
{
// Compute the sum of log(luminance) throughout the sample points
vSample = tex2D(s0, vScreenPosition+g_avSampleOffsets[iSample]);
fLogLumSum += log(dot(vSample, LUMINANCE_VECTOR)+0.0001f);
}
// Divide the sum to complete the average
fLogLumSum /= 9;
return float4(fLogLumSum, fLogLumSum, fLogLumSum, 1.0f);
}
//于是m_apTexToneMap[3]保存的就是按照3X3的方式采样得到的平均的Log值，我们的目标是计算出所有的像素的Log的
平均值然后exp,我们下一部就是利用每次的缩小，取得更大范围的平均值，最后到4X4得贴图，我们在采样这最后的16个像素，然
exp(value/16);
//下面的循环就是完成直到4X4得求平均值的过程
while( dwCurTexture > 0 )
{
m_apTexToneMap[dwCurTexture+1]->GetLevelDesc( 0, &desc );
GetSampleOffsets_DownScale4x4( desc.Width, desc.Height, avSampleOffsets );
m_pEffect->SetTechnique("ResampleAvgLum");
m_pEffect->SetValue("g_avSampleOffsets", avSampleOffsets, sizeof(avSampleOffsets));
m_pd3dDevice->SetRenderTarget(0, apSurfToneMap[dwCurTexture]);
m_pd3dDevice->SetTexture(0, m_apTexToneMap[dwCurTexture+1]);
m_pd3dDevice->SetSamplerState( 0, D3DSAMP_MAGFILTER, D3DTEXF_POINT );
m_pd3dDevice->SetSamplerState( 0, D3DSAMP_MINFILTER, D3DTEXF_POINT );
....
dwCurTexture--;
}
//这个部分的shader操作如下
float4 SampleLumIterative(in float2 vScreenPosition : TEXCOORD0) : COLOR
{
float fResampleSum = 0.0f;
for(int iSample = 0; iSample < 16; iSample++)
{
// Compute the sum of luminance throughout the sample points
fResampleSum += tex2D(s0, vScreenPosition+g_avSampleOffsets[iSample]);
}
// Divide the sum to complete the average
fResampleSum /= 16;
return float4(fResampleSum, fResampleSum, fResampleSum, 1.0f);
}
//每次的操作都使用上次的结果作为Texture
//最后一步就是计算我们的exp(value/16);
m_pEffect->SetTechnique("ResampleAvgLumExp");
m_pEffect->SetValue("g_avSampleOffsets", avSampleOffsets, sizeof(avSampleOffsets));
m_pd3dDevice->SetRenderTarget(0, apSurfToneMap[0]);
m_pd3dDevice->SetTexture(0, m_apTexToneMap[1]);
m_pd3dDevice->SetSamplerState( 0, D3DSAMP_MAGFILTER, D3DTEXF_POINT );
m_pd3dDevice->SetSamplerState( 0, D3DSAMP_MINFILTER, D3DTEXF_POINT );
//相应的shader操作是:
float4 SampleLumFinal(in float2 vScreenPosition : TEXCOORD0) : COLOR
{
float fResampleSum = 0.0f;
for(int iSample = 0; iSample < 16; iSample++)
{
// Compute the sum of luminance throughout the sample points
fResampleSum += tex2D(s0, vScreenPosition+g_avSampleOffsets[iSample]);
}
// Divide the sum to complete the average, and perform an exp() to complete
// the average luminance calculation
fResampleSum = exp(fResampleSum/16);
return float4(fResampleSum, fResampleSum, fResampleSum, 1.0f);
}
//这样我们就得到场景的平均亮度m_apTexToneMap[0]这个1X1的贴图里面。
