OpenGL versions 3.x and above have a set of required image formats that all conforming implementations must implement.
#Pass mouse coordinates to behavior class driver
If the OpenGL implementation does not support the particular format and precision you choose, the driver will internally convert it into something it does support. It is preferred to actually give a real image format, one with a specific internal precision.
The X refers to the number of components ( GL_RED would be 1, GL_RG would be 2, GL_RGB would be 3, GL_RGBA would be 4). You can (but it is not advisable to do so) call glTexImage2D(GL_TEXTURE_2D, 0, X, width, height, 0, format, type, pixels) and you set X to 1, 2, 3, or 4. If your intention really is to work with packed RGB/BGR data, you should set the alignment to 1 (or preferably, consider switching to RGBA/BGRA.) The GL_PACK/UNPACK_ALIGNMENTs can only be 1, 2, 4, or 8. If you read it in a format such as GL_BGR or GL_RGB then you risk running into this problem. If you read the buffer with a format such as GL_BGRA or GL_RGBA you won't have any problems since the line will always be a multiple of 4. The default alignment is again 4 which means each horizontal line must be a multiple of 4 in size. There is a GL_PACK_ALIGNMENT just like the GL_UNPACK_ALIGNMENT. Similarly, if you read a buffer with glReadPixels, you might get similar problems. This means, the driver converts your GL_RGB or GL_BGR to what the GPU prefers, which typically is RGBA/BGRA. GL_RGB and GL_BGR is considered bizarre since most GPUs, most CPUs and any other kind of chip don't handle 24 bits. In other words, GL_RGBA or GL_BGRA is preferred when each component is a byte. The default alignment is 4.Īnd if you are interested, most GPUs like chunks of 4 bytes. This is done by calling glPixelStorei(GL_UNPACK_ALIGNMENT, #), where # is the alignment you want.
OpenGL's row alignment can be changed to fit the row alignment for your image data. For those that don't, each row will start exactly 1203 bytes from the start of the last. Some image file formats may inherently align each row to 4 bytes, but some do not. If we do the math, 401 pixels x 3 bytes = 1203, which is not divisible by 4. The height is irrelevant what matters is the width. This typically happens to users loading an image that is of the RGB or BGR format (for example, 24 BPP images), depending on the source of your image data.Įxample, your image width = 401 and height = 500. If your program crashes during the upload, or diagonal lines appear in the resulting image, this is because the alignment of each horizontal line of your pixel array is not multiple of 4. You create storage for a Texture and upload pixels to it with glTexImage2D (or similar functions, as appropriate to the type of texture). MyTexture :: MyTexture ( const char * pfilePath ) Texture upload and pixel reads For example, one might have a texture object that has a constructor and a destructor like the following: In an object-oriented language like C++, it is often useful to have a class that wraps an OpenGL Object. In case of a core extension, you should check for both the version and the presence of the extension if either is there, you can use the functionality. The correct behavior is to check for the presence of the extension if you want to use the extension API, and check the GL version if you want to use the core API. One of the possible mistakes related to this is to check for the presence of an extension, but instead using the corresponding core functions. Common Mistakes when using deprecated functionality.Mistakes related to measuring Performance.Unexpected Results you can get when using OpenGL.There are also other articles explaining common mistakes: 31 glGetFloatv glGetBooleanv glGetDoublev glGetIntegerv.30 Disable depth test and allow depth writes.22 Selection and Picking and Feedback Mode.9 Checking For Errors When You Compile Your Shader.
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