glreadpixels

I'm trying to copy vertex data from a texture to a vertex buffer, and then draw the vertex buffer. As far as I know the best way to do this is to bind the texture to a fbo, and use glReadPixels to copy it to a vbo. However, I can't seem to get this working: glReadPixels fails with the error "invalid operation". Corrections, examples and alternate methods welcome. :) Here's the relevant code: glEnable(GL_TEXTURE_2D) w, h = 32, 32 vbo = glGenBuffers(1) glBindBuffer(GL_ARRAY_BUFFER, vbo) glBufferData(GL_ARRAY_BUFFER, sizeof(c_float)*w*h*4, None, GL_STREAM_COPY) glBindBuffer(GL_ARRAY_BUFFER, 0)

This question already has answers here : Closed 7 years ago . Possible Duplicate: Why is glReadPixels() failing in this code in iOS 6.0? I currently have an App in Appstore that uses the Cocos2D framework. For collision detection I am using glReadPixels. The screen only has white and black pixels and detecting a black pixel means collision. Everything works fine up to iOS 5.1.1 but in iOS6 Beta (all of them) glReadPixels stopped working. Now the RGB values returned by glReadPixels are always 0,0,0. Does anyone have an idea what went wrong or how to fix that? Your help is much appreciated!

How to take a screenshot of an OpenGL window in C++ and save it to file. I found the glReadPixels() function, but I don't know what to do next. Where I can set path to a file, for example? If not difficult, write code, please. huy This piece of code captures the OpenGL window and export to a BMP file. You must have FreeImage library to run it. // Make the BYTE array, factor of 3 because it's RBG. BYTE* pixels = new BYTE[3 * width * height]; glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, pixels); // Convert to FreeImage format & save to file FIBITMAP* image = FreeImage

I'm trying to detect the opengl object under the cursor... I have read it referred to as picking. Here is my code: public int makeBuffer(GL10 gl, int x, int y) { ByteBuffer PixelBuffer = ByteBuffer.allocateDirect(4); PixelBuffer.order(ByteOrder.nativeOrder()); PixelBuffer.position(0); int mTemp = 0; gl.glReadPixels((int)x, (int) y, 1, 1, GL10.GL_RGBA, GL10.GL_UNSIGNED_BYTE, PixelBuffer); Log.e("Picking", " xy: x" + x + " y"+ y); byte b [] = new byte[4]; PixelBuffer.get(b); Log.e("Picking", " rgba: r"+ PixelBuffer.get(0) + " g" + PixelBuffer.get(1) + " b" + PixelBuffer.get(2) + " a" +

I want to improve glReadPixels() performance using PBO (for GLES 3 devices) and I ran into a problem in this piece of code: final ByteBuffer pboByteBuffer = ByteBuffer.allocateDirect(4 * mWidth * mHeight); pboByteBuffer.order(ByteOrder.nativeOrder()); //set framebuffer to read from GLES30.glReadBuffer(GLES30.GL_BACK); // bind pbo GLES30.glBindBuffer(GLES30.GL_PIXEL_PACK_BUFFER, mPboHandleContainer[0]); // read pixels(should be instant) GLES30.glReadPixels(0, 0, mWidth, mHeight, GLES30.GL_RGBA, GLES30.GL_UNSIGNED_BYTE, pboByteBuffer); // map pbo to bb ByteBuffer byteBuffer = ((ByteBuffer)