我看到一个多通道、多 RT 乒乓渲染的奇怪问题
我正在使用 3 个着色器和一个 FBO，在任何阶段都没有错误。我使用的是opengl 4，所以我没有使用glBegin/glEnd，我使用我自己的矩阵进行转换，我使用顶点缓冲区进行渲染
该测试的总体思路是为三个单独的 fbo 附件渲染 3 种不同的颜色（我意识到在第一遍中两次渲染 vbo 效率不高，但这只是为了帮助我理解其他来源中的问题）然后将一组单独的纹理绑定到 fbo 并使用第一组作为采样器。最后一步是将结果混合到后台缓冲区中
奇怪的是，当第一个应该是红色而第二个应该是绿色（因为这些值来自第二个着色器）时，两个四边形的输出都显示为红色。
如果我将第二个着色器中的 SamplePix 函数更改为始终从第二个采样器中获取，则两者都显示为绿色，如果从第三个采样器中查找，则全部显示为黄色，但它似乎只能从一个采样器中读取。
现在我似乎无法解释为什么我可以从每个采样器中读取，但循环似乎没有正确查找（在着色器 2 中）
此外，如果我切换到渲染在着色器 2 中采样的纹理，我会在第二遍中看到黑色四边形（图 2）
希望有人可以对这个问题有所了解。（我也尝试在第一次通过后添加一个同步围栏对象，但这并没有什么不同）
纹理样本：
// initial setup of shaders and vertex buffers ommitted for now (in separate source files)
// fbo setup like so
const int DepthLayers = 3;
bool InitFBO()
{
// width and height 768pixels
for (int j=0; j<DepthLayers; j++)
{
const int idx = j + (DepthLayers*i);
glGenTextures(1, &g_FBOManager.m_fboTex[ idx ]);
glBindTexture(GL_TEXTURE_2D, g_FBOManager.m_fboTex[ idx ]);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
//no mipmaps
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, g_XMLSettings->WWidth(), g_XMLSettings->WHeight(), 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
//depth
glGenTextures(1, &g_FBOManager.m_fboDepthTex[ idx ]);
glBindTexture(GL_TEXTURE_2D, g_FBOManager.m_fboDepthTex[ idx ]);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
//no mipmaps
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_DEPTH_TEXTURE_MODE, GL_INTENSITY);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_MODE, GL_NONE/* GL_COMPARE_R_TO_TEXTURE*/);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_COMPARE_FUNC, GL_LEQUAL);
glTexImage2D( GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT32, g_XMLSettings->WWidth(), g_XMLSettings->WHeight(), 0, GL_DEPTH_COMPONENT, GL_FLOAT, 0);
glBindTexture(GL_TEXTURE_2D, g_FBOManager.m_fboDepthTex[idx]);
pglFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT,GL_TEXTURE_2D, g_FBOManager.m_fboDepthTex[idx], 0);
glBindTexture(GL_TEXTURE_2D, g_FBOManager.m_fboTex[idx]);
// attach a texture to FBO color attachment point
pglFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, g_FBOManager.m_fboTex[idx], 0);
// check FBO status
pglBindFramebufferEXT( GL_FRAMEBUFFER_EXT, g_FBOManager.FboId(i) );
if(!CheckFramebufferStatus())
{
return false;
}
}
BindFrameBuffer(-1); // unbind fbo
if (GLGETERROR("1", fileBuf, lineBuf)) ; // check for glErrors
return true; // all ok
}
// code to init second set of textures before the render loop
const int w = g_XMLSettings->WWidth(); //res: 768 square
const int h = g_XMLSettings->WHeight();
glGenTextures(bufCount, &ttex[0]);
for (int i=0; i<bufCount; ++i)
{
glBindTexture(GL_TEXTURE_2D, ttex[i]);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8, w, h, 0, GL_RGBA, GL_UNSIGNED_BYTE, 0);
}
const int bufCount = 3;
void EnableTexture1()
{
glActiveTextureARB(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, g_BackTexture);
glUniform1iARB(g_pPassAShader->m_clr_idx, 0);
}
void RenderLoop()
{
GLenum buffers[] = { GL_COLOR_ATTACHMENT0_EXT, GL_COLOR_ATTACHMENT1_EXT, GL_COLOR_ATTACHMENT2_EXT };
glColor4f(0.0f, 0.0f, 0.0f, 0.0f);
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);
glUseProgramObjectARB(g_pPassAShader->m_glContext);
EnableTexture1();
//... code omitted to set transform matrix and supply to shader
if (!BindFrameBuffer(0))
assert(0);
const GLuint DTex = g_FBOManager.GetDepthTexture(0);
glBindTexture(GL_TEXTURE_2D, DTex);
pglFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT,GL_TEXTURE_2D, DTex, 0);
for (UINT i=0; i<bufCount; ++i)
{
glBindTexture(GL_TEXTURE_2D, g_FBOManager.GetTexture(i));
pglFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT + i, GL_TEXTURE_2D, g_FBOManager.GetTexture(i), 0);
if (!CheckFramebufferStatus())
assert(0);
}
glDrawBuffers(bufCount,buffers);
// this is very important! if we don't clear it won't get written to
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glDisable(GL_BLEND);
EnableTexture1();
RenderVertexCache(0);
//... code omitted to set transform matrix and supply to shader
// render the second quad to other FBO tex
RenderVertexCache(0);
DisableShader(0);
BindFrameBuffer(-1); // unbinds fbo
//pass 2
if (!BindFrameBuffer(0))
assert(0);
// bind other set of textures to the fbo
for (UINT i=0; i<bufCount; ++i)
{
glBindTexture(GL_TEXTURE_2D,ttex[i]);
pglFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT + i, GL_TEXTURE_2D, ttex[i], 0);
if (!CheckFramebufferStatus())
assert(0);
}
glDrawBuffers(bufCount,buffers);
// this is very important! if we don't clear it won't get written to
glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );
// bind our set from prev pass to the samplers as input
glUseProgramObjectARB(g_pPassBShader->m_glContext);
for (UINT i=0; i<bufCount; ++i)
{
glActiveTextureARB(GL_TEXTURE0+i);
glBindTexture(GL_TEXTURE_2D,g_FBOManager.GetTexture(i));
glUniform1iARB(g_pPassBShader->m_intex_idx[i], i);
}
VertexBufferManager2::RenderUsingOrthoEx(g_pPassBShader); // renders a full screen quad
DisableShader(0);
BindFrameBuffer(-1);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
// pass 3
glUseProgramObjectARB(g_pPassCShader->m_glContext);
for (UINT i=0; i<bufCount; ++i)
{
glActiveTextureARB(GL_TEXTURE0+i);
glBindTexture(GL_TEXTURE_2D, ttex[i]);
glUniform1iARB(g_pPassCShader->m_intex_idx[i], i);
}
VertexBufferManager2::RenderUsingOrthoEx(g_pPassCShader);
if (GLGETERROR("at1", fileBuf, lineBuf)) ; // reports any glErrors
}
// the three shaders (fragment shaders only)
// vertex shaders transfer uv's and transform vertices (version set to 410 in all)
// shader for pass1
//--------------------------------------------------------------------------------------------
//--------------------------------------------------------------------------------------------
#version 410
uniform sampler2D g_ClrMap;
in vec2 g_InterpUV; // supplied by vshader
out vec4 g_FBOLayers[ 3 ];
void main(void)
{
vec4 tex = texture(g_ClrMap, g_InterpUV); // if we set fbo from texture only first texture renders
g_FBOLayers[0] = vec4(1,0,0,.5);
g_FBOLayers[1] = vec4(0,1,0,1);
g_FBOLayers[2] = vec4(1,1,0,1);
}
// shader pass 2
//--------------------------------------------------------------------------------------------
//--------------------------------------------------------------------------------------------
#version 410
uniform sampler2D g_inLayers0;
uniform sampler2D g_inLayers1;
uniform sampler2D g_inLayers2;
in vec2 g_InterpUV ;
out vec4 g_FBOLayers[ 3 ];
vec2 fTextureSize;
vec4 SamplePix(in int buf, in vec2 tCoords, in float lod)
{
if (buf==1)
return textureLod(g_inLayers1, tCoords, lod);
else if (buf==2)
return textureLod(g_inLayers2, tCoords, lod);
return textureLod(g_inLayers0, tCoords, lod);
}
void main(void)
{
ivec2 iCoords = ivec2(int(gl_FragCoord.x),int(gl_FragCoord.y));
ivec2 iTextureSize = textureSize(g_inLayers0,0);
fTextureSize = vec2(float(iTextureSize.x), float(iTextureSize.y));
vec2 coords = vec2(gl_FragCoord.x/iTextureSize.x,gl_FragCoord.y/iTextureSize.y);
for(int i=0; i<3; ++i)
{
g_FBOLayers[i] = vec4(0.,0.,0.,0.);
}
int j = 0;
for(; j < 2; ++j)
{
g_FBOLayers[j] = SamplePix(j,coords,0);
}
}
// shader pass 3
//--------------------------------------------------------------------------------------------
//--------------------------------------------------------------------------------------------
#version 410
uniform sampler2D g_inLayers0;
uniform sampler2D g_inLayers1;
uniform sampler2D g_inLayers2;
in vec2 g_InterpUV ;
out vec4 g_PixColour;
vec4 tFetch(in int buf, in ivec2 tCoords, in int lod)
{
if (buf==1)
return texelFetch(g_inLayers1, tCoords, lod);
if (buf==2)
return texelFetch(g_inLayers2, tCoords, lod);
return texelFetch(g_inLayers0, tCoords, lod);
}
void main(void)
{
ivec2 iCoords = ivec2(int(gl_FragCoord.x),int(gl_FragCoord.y));
ivec2 iTextureSize = textureSize(g_inLayers0,0);
vec2 coords = vec2(gl_FragCoord.x/iTextureSize.x,gl_FragCoord.y/iTextureSize.y);
vec4 colour = vec4(0.,0.,0.,0.);
int i = 0;
for(; i <2; ++i) // 3rd texture omitted for now
{
vec4 texel = tFetch(i,iCoords,0);
if(texel.a + colour.a <= 1.0)
{
colour.rgb += (texel.rgb*texel.a);
colour.a += texel.a;
}
else
{
texel.a -= (texel.a + colour.a) - 1.0;
colour.rgb += (texel.rgb*texel.a);
colour.a += texel.a;
break;
}
}
g_PixColour = colour;
}