I am trying to render to multiple textures as COLOR_ATTACHMENT
s without success. All I get from displaying them is a black screen (with a red clear fill) meaning my texture is read but is 'empty'.
My pseudo code is : attach 3 textures to an FBO with texture indexes 1, 2 and 3 and color attachments 0, 1 and 2 respectively. As a test case, I tried to render my scene to the 3 color attachments so they are supposed to hold the same exact data. Then read either of those textures at shader pass 2 (with a 2Dsampler) and display them on a quad.
My original intent for those 2 extra color attachments is to use them as random data buffers using the GPU ping-pong technique. So far I just use them as texture clones for testing purpose.
When trying to read from GL_TEXTURE1
(COLOR_ATTACHMENT0
) things go fine but not from the other 2 (black screen).
The code :
// Texture indices - inside a 'myGlut' struct
GLenum skyboxTextureIndex = GL_TEXTURE0;
GLenum colorTextureIndex = GL_TEXTURE1;
unsigned int colorTextureIndexInt = 1;
GLenum depthTexture1Index = GL_TEXTURE2;
unsigned int depthTexture1IndexInt = 2;
GLenum depthTexture2Index = GL_TEXTURE3;
unsigned int depthTexture2IndexInt = 3;
//** Below is inside 'main()' **//
// Create frame buffer
myGlut.frameBuffer = glutils::createFrameBuffer();
// Create texture to hold color buffer
glActiveTexture(myGlut.colorTextureIndex);
glBindTexture(GL_TEXTURE_2D, myGlut.colorTexture);
myGlut.colorTexture = glutils::createTextureAttachment(myGlut.camera -> getRenderResizedWidthPx(), myGlut.camera -> getRenderResizedHeightPx());
glutils::bindTextureAttachment(GL_COLOR_ATTACHMENT0, myGlut.colorTexture);
// Create 1st texture to hold depth buffer wannabe :>
glActiveTexture(myGlut.depthTexture1Index);
glBindTexture(GL_TEXTURE_2D, myGlut.depthTexture1);
myGlut.depthTexture1 = glutils::createTextureAttachment(myGlut.camera -> getRenderResizedWidthPx(), myGlut.camera -> getRenderResizedHeightPx());
glutils::bindTextureAttachment(GL_COLOR_ATTACHMENT1, myGlut.depthTexture1);
// Create 2nd texture to hold depth buffer wannabe :>
glActiveTexture(myGlut.depthTexture2Index);
glBindTexture(GL_TEXTURE_2D, myGlut.depthTexture2);
myGlut.depthTexture2 = glutils::createTextureAttachment(myGlut.camera -> getRenderResizedWidthPx(), myGlut.camera -> getRenderResizedHeightPx());
glutils::bindTextureAttachment(GL_COLOR_ATTACHMENT2, myGlut.depthTexture2);
// Check FBO
if (!glutils::checkFBOStatus()) return 0;
With glutils::
functions
// Clear screen
void glutils::clearScreen (float r, float g, float b, float a) {
glClearColor(r, g, b, a);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
}
// Bind select framebuffer
void glutils::bindFrameBuffer(int frameBuffer, int width, int height) {
glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer);
glViewport(0, 0, width, height);
}
// Create frame buffer
GLuint glutils::createFrameBuffer() {
GLuint frameBuffer;
glGenFramebuffers(1, &frameBuffer);
glBindFramebuffer(GL_FRAMEBUFFER, frameBuffer);
return frameBuffer;
}
// Create a texture attachment
GLuint glutils::createTextureAttachment(int width, int height) {
GLuint texture;
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, NULL);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
return texture;
}
// Bind a texture attachment to select framebuffer
void glutils::bindTextureAttachment (GLenum colorAttachment, GLuint texture) {
glFramebufferTexture2D(GL_FRAMEBUFFER, colorAttachment, GL_TEXTURE_2D, texture, 0);
}
// Check current frame buffer status
bool glutils::checkFBOStatus () {
if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
std::cerr << "##### ERROR : Frambuffer not complete... #####" << std::endl;
return false;
}
else return true;
}
Then the glut display func :
// Clear screen
glutils::clearScreen(1.f, 0.f, 0.f, 1.f);
// Bind to custom framebuffer
glutils::bindFrameBuffer(myGlut.frameBuffer, myGlut.camera -> getScreenWidthPx(), myGlut.camera -> getScreenHeightPx());
// Set draw context
GLuint drawBuffers[2];
if (myGlut.depthTextureSwitch) { drawBuffers[0] = GL_COLOR_ATTACHMENT0;
drawBuffers[1] = GL_COLOR_ATTACHMENT2;
} else { drawBuffers[0] = GL_COLOR_ATTACHMENT0;
drawBuffers[1] = GL_COLOR_ATTACHMENT1;
} glDrawBuffers(2, drawBuffers);
// Use main program and bind uniforms
glUseProgram(myGlut.theProgram);
myGlut.refreshUniformsPass_1();
// Draw quad to sample
glutils::drawQuad();
// Unbind custom framebuffer -> use default (screen)
glutils::unbindCurrentFrameBuffer(myGlut.camera -> getScreenWidthPx(), myGlut.camera -> getScreenHeightPx());
// Use secondary program and bind uniforms
glUseProgram(myGlut.theProgram2);
myGlut.refreshUniformsPass_2();
// Draw quad to apply texture to
glutils::drawQuad();
// Switch
myGlut.depthTextureSwitch = !myGlut.depthTextureSwitch;
// Display & loop
glutSwapBuffers();
glutPostRedisplay();
Relevant uniform bindings -> pass 1
glUniform1i(glGetUniformLocation(myGlut.theProgram, "depthTexture"), !myGlut.depthTextureSwitch ? myGlut.depthTexture2IndexInt : myGlut.depthTexture1IndexInt);
Relevant shader code -> Pass 1
layout (location = 0) out vec4 outputColor;
layout (location = 1) out vec4 outputDepth1;
layout (location = 2) out vec4 outputDepth2;
uniform sampler2D depthTexture;
void main() {
// ...
outputColor = someColor;
outputDepth1 = someColor;
outputDepth2 = someColor;
}
Relevant uniform bindings -> pass 2
glUniform1i(glGetUniformLocation(myGlut.theProgram2, "texFramebuffer"), myGlut.depthTextureSwitch ? myGlut.depthTexture1IndexInt : myGlut.depthTexture2IndexInt);
With relevant shader code -> pass 2
uniform sampler2D texFramebuffer;
out vec4 outputColor;
// ...
void main() {
outputColor = texture(texFramebuffer, vec2(gl_FragCoord.x / screenWidthPx * resRatio, gl_FragCoord.y / screenHeightPx * resRatio));
}
In a nutshell : my GL_TEXTURE0
holds the scene while GL_TEXTURE1
and GL_TEXTURE2
are black. Why ?
I finally found the culprit. Because I am binding the framebuffer inside the looped display()
function, I needed to bind texture attachments as well after I bound the FBO. Changing to
// Bind to custom framebuffer
glutils::bindFrameBuffer(myGlut.frameBuffer, myGlut.camera -> getScreenWidthPx(), myGlut.camera -> getScreenHeightPx());
// Bind to select attachments
glutils::bindTextureAttachment(GL_COLOR_ATTACHMENT0, myGlut.colorTexture);
if (!myGlut.depthTextureSwitch) glutils::bindTextureAttachment(GL_COLOR_ATTACHMENT1, myGlut.depthTexture1);
else glutils::bindTextureAttachment(GL_COLOR_ATTACHMENT1, myGlut.depthTexture2);
allowed me to render to all needed color attachments.
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