I need to load PNGs and JPGs to textures. I also need to save textures to PNGs. When an image exceeds GL_MAX_TEXTURE_SIZE I need to split the image into separate textures.
I want to do this with C++.
What could I do?
Thank you.
I need to load PNGs and JPGs to textures
SDL_Image
Qt 4
or use libpng and libjpeg directly (you don't really want to do that, though).
When an image exceeds GL_MAX_TEXTURE_SIZE I need to split the image into separate textures.
You'll have to code it yourself. It isn't difficult.
DevIL can load and save many image formats including PNG and JPEG. It comes with helper functions that upload these images to OpenGL textures (ilutGLBindTexImage, ilutGLLoadImage) and functions to copy only parts of an image to a new image (ilCopyPixels, can be used to split large textures).
For the loading part SOIL looks rather self-contained.
Related
Here's what I want to do: I want to load a plain image file (.png, .tga, .bmp, etc), upload this image to OpenGL as a texture, tell OpenGL to generate mipmaps for the texture, tell OpenGL to compress the image (with S3TC/RGTC), then download the entire compressed/mipmapped texture, save it into a file, and later be able to load the entire texture into OpenGL at once.
I've already managed the first 3 steps. I use SDL2_Image to handle image loading, I can upload said image via glTexImage2D(), and I can create mipmaps using glGenerateMipmap(). From there, I'm pretty much lost, but I can figure out how to compress the images without much trouble.
What I need help with is the final bit - downloading the entire compressed+mipmapped texture as a single, contiguous block of data, saving it to file (at the content authoring stage), and later uploading the whole thing at once (at runtime). Any advice for where I can start?
PS. I'm using OpenGL 3.3 as my minimum version.
You can compress to S3TC or DXT using rygDXT real time compressor, because there is no DXT compression embedded in the driver. Most DXT compressors are offline (not real time) and needs seconds or minutes to run.
You also have nvdxt, nvidia SDK provides full code sample to compress textures in DXT but its slow I warn you. ryg DXT should be faster.
Then for upward copy you should be able to copy the texture into a dynamic ("staging" in DX terms) buffer and then map the dynamic buffer to memory using some lock (glMapBuffer?) then memcopy.
In OpenGL you could read a BMP file and use it as texture.
I know how to read a BMP file in OPENGL.
I just want to know if is it the same thing with JPG or JPEG files? is OpenGL support those files?
OpenGL does not support BMP files. It just cares about raw image date as one-, two or threedimensional arrays of pixel data with up to 4 channels (and a set of different data types). OpenGL does not even know what a file is. And it can't load anything. If you need JPEG files, you have to load them via other means, like libjpeg or some higher level image loading libraries or some of the other image loading libraries.
What is the easiest format to read a texture into opengl? Are there any tutorials -good tutorials, for loading image formats like jpg, png, or raw into an array which can be used for texture mapping (preferably without the use of a library like libpng)?
OpenGL itself does not knows nothing about common image formats (other than natively supported S3TC/DXT compressed and alikes, but they are a different story). You need to expand you source images into RGBA arrays. Number of formats and combinations are supported. You need to choose one that suits you, e.g. GL_ALPHA4 for masks, GL_RGB5_A1 for 1bit transparency, GL_BGRA/GL_RGBA for fullcolor, etc.
For me the easiest (not the fastest) way are PNGs, for their lossless compression and full Alpha support. I read the PNG and write RGBA values into array which I then hand over to OpenGL texture creation. If you don't need alpha you may as well accept JPG or BMP. Pipeline is common Source -> Expanded RGBA array -> OpenGL texture.
There is a handy OpenGL texture tutorial available at the link: http://www.nullterminator.net/gltexture.html
How can I "draw"\"merge" a png top of another png (background) using libpng, while keeping the alpha section of the png being drawn on top of the backhround png. There does not seem to be any tutorials or anything mentioned in the documentation about it.
libpng is a library for loading images stored in the PNG file format. It is not a library for blitting images, compositing images, or anything of that nature. libpng's basic job is to take a file or memory image and turn it into an array of color values. What you're talking about is very much out of scope for libpng.
If you want to do this, you will have to do the image composition yourself manually. Or use a library that can do image composition (cairo, etc).
I'm having a few issues regarding how to render a PVR.
I'm confused about how to get the data from the PVR to screen. I have a window that is ready to draw a picture and I'm a bit stuck. What do I need to get from the PVR as parameters to then be able to draw a texture? With jpeg and pngs locally you can just load the image from a directory but how would the same occur for a PVR?
Depends what format the data inside the PVR is in. If it's a supported standard then just copy it to a texture with glTexSubImage2D(), otherwise you will need to decompress it into something OpenGL understands - like RGB or RGBA.
edit - OpenGL is a display library (well much much more than that), it doesn't read images, decode movies or do sound.
TGA files are generally very simple uncompressed RGB or RGBA image data, it should be trivial to decode the file, extract the image data and copy it directly to an opengl texture.
since you tagged the question Qt you can use QImage to load the tga and Using QImage with OpenGL