Have anyone tried this (how-can-i-use-a-dynamically-sized-texture-array-with-glteximage2d) with glTexSubImage2D instead? I really need it and I can't put it to work properly, all I get is a striped, funny coloured square on my original texture.
What do you mean, you need it ?
glTexSubImage2D redefines a contiguous
subregion of an existing
two-dimensional texture image.
What that means is that you need to specify the size of your texture with glTexImage2D. That is what that API is for.
glTexSubImage2D is only there to update (parts of) the contents of an already defined Texture.
glTexSubImage2D does not resize your texture.
All it does is update a rectangle of your existing texture with new texels/pixels.
If you need to change the size of your texture you will need to create a new texture of the correct size and discard the old one.
Related
I want to display a 2D array of pixels directly to the screen. The pixel-data is not static and changes on user triggered event like a mousemove. I wish to have a display framebuffer to which I could write directly to the screen.
I have tried to create a texture with glTexImage2D(). I then render this texture to a QUAD. And then I update the texture with glTexSubImage2D() whenever a pixel is modified.
It works!
But this is not the efficient way I guess. The glTexSubImage2D copies whole array including the unmodified pixels back to the texture which is not good performance wise.
Is there any other way, like having a "display-framebuffer" to which I could write only the modified pixels and change will reflect on the screen.
glBlitFramebuffer is what you want.
Copies a rectangular block of pixels from one frame buffer to another. Can stretch or compress, but doesn't go through shaders and whatnot.
You'll probably also need some combination of glBindFramebuffer, glFramebufferTexture, glReadBuffer to set up the source and destination.
On OpenGL, I'm using glTexSubImage2d to overwrite specific parts of a 2D texture with rectangular sprites. Those sprites have, though, some transparent pixels (0x00000000) that I want to be ignored - that is, I don't want those pixels to overwrite whatever is on their positions on the target texture. Is there any way to tell OpenGL not to overwrite those pixels?
This must be compatible with OpenGL versions as low as possible.
No, the glTexSubImage2d will copy the data to the texture directly no matter what the source or the target is.
I can only suggest you to create another texture with the data you are trying to push using glTexSubImage2d and then draw this texture to your target texture. This will lead to a pretty standard drawing pipeline so you can do whatever you want using blend functions or shaders.
I want to create an openGL 2D texture and set the RGBA values of every pixel by its own. Can someone give me an explanation for my problem? I didn't find one in the internet.
If you're just looking to write the pixels of a 2D texture, you can simply use glTexImage2D, which takes a buffer specifying the pixel data you wish to upload to the texture (https://www.opengl.org/sdk/docs/man/html/glTexImage2D.xhtml). Alternatively, you can use glTexSubImage2D to write a portion of the texture's pixels (https://www.khronos.org/opengles/sdk/docs/man/xhtml/glTexSubImage2D.xml). If you're instead looking to do the analogous thing with the framebuffer, you can use glDrawPixels (https://www.opengl.org/sdk/docs/man2/xhtml/glDrawPixels.xml).
If the target is the backbuffer, attempting to draw to a exact pixel values to a texture by binding it as a framebuffer, and then rendering a textured quad completely covering it is possible. However, this process is subject to blending and potentially pixel-center issues, whereas glDrawPixels is not.
I did something like this some time ago, when playing around with OpenGL.
Have a look at the code here, on GitHub.
You can find it in main.cpp.
Basically, my idea was to create an array of floats, set the values, copy to GPU with glBufferData and draw with glDrawElements.
As I remember it, doing it often was very bad in terms of performance, so it's probably not the best direction.
Please also note that this code is just my sandbox, and may not be the best possible example to be copied.
I am trying to update a small square section in a large rectangular texture.
I've tried using glTexSubImage2D with the target set to GL_TEXTURE_RECTANGLE_ARB, but I'm running into issues. It may just be that I don't know how to use glTexSubImage2D correctly though. The issues may be due to the fact that I'm trying not to load the whole texture into main memory using glTexImage2D before updating the subimage?
Can anyone tell me if it's possible to update a subimage of a rectangular texture without having to read the entire texture into main memory? I see glTexCopyTexSubImage2D... Still wondering if these methods work with rectangular textures though.
I'm quite sure you have to at least upload full-size texture even once with glTexImage2D. You can even use a blank array if you don't have any access to whole image at the beginning.
glCopyTexSubImage2D is not really like what you want. It copies a specific portion from "frame buffer" to a texture. But, you want to upload from main memory, right?
I don't see any reason why rectangular textures cannot be supported by those methods unless there is a broken driver.
Consider that rectangular textures do not use texture coordinates in [0..1] range like the other textures. Instead they use [0..Width] and [0..Height] range.
I have discovered that there are still a fair number of drivers out there that don't support NPOT textures so I'm trying to retro-fit my 2D engine (based on OpenTK, which is in turn based on OpenGL) with Texture2D support instead of relying on GL_ARB_texture_rectangle. As part of this I am forcing all NPOTS texture bitmaps to allocate extra space up to the next power-of-2 size so they won't cause errors on these drivers. My question is, do I really have to resize the real bitmap and texture and allocate all that extra memory, or is there a way to tell OpenGL that I want a power-of-2 size texture, but I'm only going to use a portion of it in the upper left?
Right now my call looks like this:
GL.TexImage2D(texTarget, 0, PixelInternalFormat.Rgba8, bmpUse.Width, bmpUse.Height, 0, PixelFormat.Bgra, PixelType.UnsignedByte, bits.Scan0);
This is after I have made bmpUse be a copy of my real texture bitmap with extra space on the right and bottom.
Use glTexImage2D with empty data to initialize the texture and glTexSubImage2D to fill a portion of it with data. Technically OpenGL allows the data parameter given to glTexImage{1,2,3}D to be a null pointer, indicating that the texture object is just to be initializd. It depends on the language binding, if that feature remains supported in the target language – just test what happens if you pass a null pointer.
datenwolf is right on how to initialize the texture with just a partial image, but there are 2 issues with this you need to be aware of:
you need to remap the texture coordinates of your mesh, as the [0-1] texture range of the full texture now also contains uninitialized data, as opposed to your full texture. The useful range is now [0-orig_width/padded_width]
wrapping of your texture will only wrap the whole texture, not your sub-part.