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I have a texture on the GPU defined by an OpenGL textureID and target.
I need for further processing a 300 pixel bitmap in CPU memory (width 300 pixel, height proportional depending on the source width).
The pixel format should be RGBA, ARGB or BGRA with float components.
How can this be done?
Thanks for your reply.
I tried the following. But I get only white pixels back:
glEnable(GL_TEXTURE_2D);
// create render texture
GLuint renderedTexture;
glGenTextures(1, &renderedTexture);
glBindTexture(GL_TEXTURE_2D, renderedTexture);
glTexImage2D(GL_TEXTURE_2D, 0,GL_RGB, (GLsizei)analyzeWidth, (GLsizei)analyzeHeight, 0,GL_RGBA, GL_FLOAT, 0);
unsigned int fbo;
glGenFramebuffers(1, &fbo);
glBindFramebuffer(GL_FRAMEBUFFER, fbo);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, renderedTexture, 0);
// draw texture
glBindTexture(GL_TEXTURE_2D, inTextureId);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
// Draw a textured quad
glBegin(GL_QUADS);
glTexCoord2f(0, 0); glVertex3f(0, 0, 0);
glTexCoord2f(0, 1); glVertex3f(0, 1, 0);
glTexCoord2f(1, 1); glVertex3f(1, 1, 0);
glTexCoord2f(1, 0); glVertex3f(1, 0, 0);
glEnd();
GLenum status = glCheckFramebufferStatus(GL_FRAMEBUFFER);
if(status == GL_FRAMEBUFFER_COMPLETE)
{
}
unsigned char *buffer = CGBitmapContextGetData(mainCtx);
glReadPixels(0, 0, (GLsizei)analyzeWidth, (GLsizei)analyzeHeight, GL_RGBA, GL_FLOAT, buffer);
glDisable(GL_TEXTURE_2D);
glBindFramebuffer(GL_FRAMEBUFFER, 0); //
glDeleteFramebuffers(1, &fbo);
Create a second texture with the size 300*width/height x 300
Create a Framebuffer Object and attach the new texture as color buffer.
Set approrpiate texture filters for the (unscaled) source texture. You have the choice between point sampling (GL_NEAREST) and bilinear filtering (GL_LINEAR). If you are downscaling by more than a factor of 2 you might consider also using mipmapping, and might want to call glGenerateMipmap on the source texture first, and use one of the GL_..._MIPMAP_... minification filters. However, the availability of mipmapping will depend on how the source texture was created, if it is an immutable texture object without the mipmap pyramid, this won't work.
Render a textured object (with the original source texture) to the new texture. Most intuitive geometry would be a viewport-filling rectangle, most efficient would be a single triangle.
Read back the scaled texture with glReadPixels (via the FBO) or glGetTexImage (directly from the texture). For improved performance, you might consider asynchronous readbacks via Pixel Buffer Objects.
I am attempting to build a simple project using immediate mode textures.
Unfortunately, when I render, the GL color shows up rather than the texture. I've searched around for solutions, but found no meaningful difference between online examples and my code.
I've reduced it to a minimal failing example, which I have provided here. If my understanding is correct, this should produce a textured quad, with corners of black, red, green, and blue. Unfortunately, it appears purple, as if it's ignoring the texture completely. What am I doing wrong?
#include <glut.h>
GLuint tex;
void displayFunc() {
glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, tex);
glBegin(GL_TRIANGLE_STRIP);
glColor3f(0.5, 0, 1);
glTexCoord2f(0.0, 0.0);
glVertex2f(-1.0, -1.0);
glTexCoord2f(1.0, 0.0);
glVertex2f(1.0, -1.0);
glTexCoord2f(0.0, 1.0);
glVertex2f(-1.0, 1.0);
glTexCoord2f(1.0, 1.0);
glVertex2f(1.0, 1.0);
glEnd();
glutSwapBuffers();
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowPosition(0, 0);
glutInitWindowSize(640, 480);
glutCreateWindow("Test");
glutDisplayFunc(displayFunc);
GLubyte textureData[] = { 0, 0, 0, 255, 0, 0, 0, 255, 0, 0, 0, 255, 255, 255, 0 };
GLsizei width = 2;
GLsizei height = 2;
glGenTextures(1, &tex);
glBindTexture(GL_TEXTURE_2D, tex);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8, width, height, 0, GL_RGB8, GL_UNSIGNED_BYTE, (GLvoid*)textureData);
glutMainLoop();
}
The output:
Also possibly worth mentioning:
I am building this project on a Mac (running El Capitan 10.11.1)
Graphics card: NVIDIA GeForce GT 650M 1024 MB
You're passing an invalid argument to glTexImage2D(). GL_RGB8 is not one of the supported values for the 7th (format) argument. The correct value is GL_RGB.
Sized formats, like GL_RGB8, are used for the internalFormat argument. In that case, the value defines both the number of components and the size of each component used for the internal storage of the texture.
The format and type parameters define the data you pass in. For these, the format only defined the number of components, while the type defines the type and size of each component.
Whenever you have problems with your OpenGL code, make sure that you call glGetError() to check for errors. In this case, you would see a GL_INVALID_ENUM error caused by your glTexImage2D() call.
I am trying to do some OpenGL ES 2.0 rendering to an image file, independent of the rendering being shown on the screen to the user. The image I'm rendering to is a different size than the user's screen. I just need a byte array of GL_RGB data. I'm familiar with glReadPixels, but I don't think it would do the trick in this case since I'm not pulling from an already-rendered user screen.
Pseudocode:
// Switch rendering to another buffer (framebuffer? renderbuffer?)
// Draw code here
// Save byte array of rendered data GL_RGB to file
// Switch rendering back to user's screen.
How can I do this without interrupting the user's display? I'd rather not have to flicker the user's screen, drawing my desired information for a single frame, glReadPixel-ing and then having it disappear.
Again, I don't want it to show anything to the user. Here's my code. Doesn't work.. am I missing something?
unsigned int canvasFrameBuffer;
bglGenFramebuffers(1, &canvasFrameBuffer);
bglBindFramebuffer(BGL_RENDERBUFFER, canvasFrameBuffer);
unsigned int canvasRenderBuffer;
bglGenRenderbuffers(1, &canvasRenderBuffer);
bglBindRenderbuffer(BGL_RENDERBUFFER, canvasRenderBuffer);
bglRenderbufferStorage(BGL_RENDERBUFFER, BGL_RGBA4, width, height);
bglFramebufferRenderbuffer(BGL_FRAMEBUFFER, BGL_COLOR_ATTACHMENT0, BGL_RENDERBUFFER, canvasRenderBuffer);
unsigned int canvasTexture;
bglGenTextures(1, &canvasTexture);
bglBindTexture(BGL_TEXTURE_2D, canvasTexture);
bglTexImage2D(BGL_TEXTURE_2D, 0, BGL_RGB, width, height, 0, BGL_RGB, BGL_UNSIGNED_BYTE, 0);
bglFramebufferTexture2D(BGL_FRAMEBUFFER, BGL_COLOR_ATTACHMENT0, BGL_TEXTURE_2D, canvasTexture, 0);
Matrix::matrix_t identity;
Matrix::LoadIdentity(&identity);
bglClearColor(1.0f, 1.0f, 1.0f, 1.0f);
bglClear(BGL_COLOR_BUFFER_BIT);
Draw(&identity, &identity, this);
bglFlush();
bglFinish();
byte *buffer = (byte*)Z_Malloc(width * height * 4, ZT_STATIC);
bglReadPixels(0, 0, width, height, BGL_RGB, BGL_UNSIGNED_BYTE, buffer);
SaveTGA("canvas.tga", buffer, width, height);
Z_Free(buffer);
// unbind frame buffer
bglBindRenderbuffer(BGL_RENDERBUFFER, 0);
bglBindFramebuffer(BGL_FRAMEBUFFER, 0);
bglDeleteTextures(1, &canvasTexture);
bglDeleteRenderbuffers(1, &canvasRenderBuffer);
bglDeleteFramebuffers(1, &canvasFrameBuffer);
Here's the solution, for anybody who needs it:
// Create framebuffer
unsigned int canvasFrameBuffer;
glGenFramebuffers(1, &canvasFrameBuffer);
glBindFramebuffer(GL_RENDERBUFFER, canvasFrameBuffer);
// Attach renderbuffer
unsigned int canvasRenderBuffer;
glGenRenderbuffers(1, &canvasRenderBuffer);
glBindRenderbuffer(GL_RENDERBUFFER, canvasRenderBuffer);
glRenderbufferStorage(GL_RENDERBUFFER, GL_RGBA4, width, height);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, canvasRenderBuffer);
// Clear the target (optional)
glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
// Draw whatever you want here
char *buffer = (char*)malloc(width * height * 3);
glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, buffer);
SaveTGA("canvas.tga", buffer, width, height); // Your own function to save the image data to a file (in this case, a TGA)
free(buffer);
// unbind frame buffer
glBindRenderbuffer(GL_RENDERBUFFER, 0);
glBindFramebuffer(GL_FRAMEBUFFER, 0);
glDeleteRenderbuffers(1, &canvasRenderBuffer);
glDeleteFramebuffers(1, &canvasFrameBuffer);
You can render to a texture, read the pixels and draw a quad with that texture (if you want to show that to the user). It should not flicker but it degrades performance obviously.
On iOS for example:
OpenGL ES Render to Texture
Reading a openGL ES texture to a raw array
I'm trying to get some shadowing effects to work in OpenGL ES 2.0 on iOS by porting some code from standard GL. Part of the sample involves copying the depth buffer to a texture:
glBindTexture(GL_TEXTURE_2D, g_uiDepthBuffer);
glCopyTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, 0, 0, 800, 600, 0);
However, it appears the glCopyTexImage2D is not supported on ES. Reading a related thread, it seems I can use the frame buffer and fragment shaders to extract the depth data. So I'm trying to write the depth component to the color buffer, then copying it:
// clear everything
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
// turn on depth rendering
glUseProgram(m_BaseShader.uiId);
// this is a switch to cause the fragment shader to just dump out the depth component
glUniform1i(uiBaseShaderRenderDepth, true);
// and for this, the color buffer needs to be on
glColorMask(GL_TRUE,GL_TRUE,GL_TRUE,GL_TRUE);
// and clear it to 1.0, like how the depth buffer starts
glClearColor(1.0f, 1.0f, 1.0f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);
// draw the scene
DrawScene();
// bind our texture
glBindTexture(GL_TEXTURE_2D, g_uiDepthBuffer);
glCopyTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 0, 0, width, height, 0);
Here is the fragment shader:
uniform sampler2D sTexture;
uniform bool bRenderDepth;
varying lowp float LightIntensity;
varying mediump vec2 TexCoord;
void main()
{
if(bRenderDepth) {
gl_FragColor = vec4(vec3(gl_FragCoord.z), 1.0);
} else {
gl_FragColor = vec4(texture2D(sTexture, TexCoord).rgb * LightIntensity, 1.0);
}
}
I have experimented with not having the 'bRenderDepth' branch, and it doesn't speed it up significantly.
Right now pretty much just doing this step its at 14fps, which obviously is not acceptable. If I pull out the copy its way above 30fps. I'm getting two suggestions from the Xcode OpenGLES analyzer on the copy command:
file://localhost/Users/xxxx/Documents/Development/xxxx.mm: error:
Validation Error: glCopyTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 0, 0,
960, 640, 0) : Height<640> is not a power of two
file://localhost/Users/xxxx/Documents/Development/xxxx.mm: warning:
GPU Wait on Texture: Your app updated a texture that is currently
used for rendering. This caused the CPU to wait for the GPU to
finish rendering.
I'll work to resolve the two above issues (perhaps they are the crux if of it). In the meantime can anyone suggest a more efficient way to pull that depth data into a texture?
Thanks in advance!
iOS devices generally support OES_depth_texture, so on devices where the extension is present, you can set up a framebuffer object with a depth texture as its only attachment:
GLuint g_uiDepthBuffer;
glGenTextures(1, &g_uiDepthBuffer);
glBindTexture(GL_TEXTURE_2D, g_uiDepthBuffer);
glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH_COMPONENT, width, height, 0, GL_DEPTH_COMPONENT, GL_UNSIGNED_INT, NULL);
// glTexParameteri calls omitted for brevity
GLuint g_uiDepthFramebuffer;
glGenFramebuffers(1, &g_uiDepthFramebuffer);
glBindFramebuffer(GL_FRAMEBUFFER, g_uiDepthFramebuffer);
glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, GL_TEXTURE_2D, g_uiDepthBuffer, 0);
Your texture then receives all the values being written to the depth buffer when you draw your scene (you can use a trivial fragment shader for this), and you can texture from it directly without needing to call glCopyTexImage2D.
I have a cube which I want to rotate. I also have a light source GL_LIGHT0. I want to rotate the cube and leave the light source fixed in its location. But the light source is rotating together with my cube. I use OpenGL ES 1.1
Here's a snippet of my code to make my question more clear.
GLfloat glfarr[] = {...} //cube points
GLubyte glubFaces[] = {...}
Vertex3D normals[] = {...} //normals to surfaces
const GLfloat light0Position[] = {0.0, 0.0, 3.0, 0.0};
glLightfv(GL_LIGHT0, GL_POSITION, light0Position);
glEnable(GL_LIGHT0);
for(i = 0; i < 8000; ++i)
{
if (g_bDemoDone) break;
glLoadIdentity();
glTranslatef(0.0,0.0, -12);
glRotatef(rot, 0.0, 1.0,1.0);
rot += 0.8;
glClearColor(0, 0, 0, 1);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_NORMAL_ARRAY);
glNormalPointer(GL_FLOAT, 0, normals);
glVertexPointer(3, GL_FLOAT, 0, glfarr);
glDrawElements(GL_TRIANGLES, 3*12, GL_UNSIGNED_BYTE, glubFaces);
glDisableClientState(GL_NORMAL_ARRAY);
glDisableClientState(GL_VERTEX_ARRAY);
eglSwapBuffers(eglDisplay, eglSurface);
}
Thanks.
Fixed in relation to what? The light position is transformed by the current MODELVIEW matrix when you do glLightfv(GL_LIGHT0, GL_POSITION, light0Position);
If you want it to move with with the cube you'll have to move glLightfv(GL_LIGHT0, GL_POSITION, light0Position); to after the translation and rotation calls.
The problem seems to be that you're rotating the modelview matrix, not the cube itself. Essentially, you're moving the camera.
In order to rotate just the cube, you'll need to rotate the vertices that make up the cube. Generally that's done using a library (GLUT or some such) or simple trig. You'll be operating on the vertex data stored in the array, before the glDrawElements call. You may/may not have to or want to modify the normals or texture coordinates, it depends on your effects and how it ends up looking.