I have read around on this, including Nehe and here for solutions, but I cant find a specific answer.
I am trying to load a a photo, called stars.jpg. I want to make this my background of the scene, by mapping it using uv coordinates, doing it by
glBegin(GL_QUADS);
glTexCoord2f(0,0);
glVertex2f(0,0);
However I am just very confused about how to load the actual textures in, all the calls for
glActiveTexture();
glEnable(GL_TEXTURE_2d);
glBindTexture(GL_TEXTURE);
All they do is confuse me, what do all these mean/do, and in what order am I suppose to put these in, in order to get the stars.jpg to be my background?
Your number-one tool for loading textures in OpenGL is the Simple OpenGL Image Loader (SOIL) library. You just need to pass the filename and some flags and you'll get your texture ID.
Also, you're learning very old and outdated version of OpenGL now - you might want to have a google for newer tutorials or browse the specs whenever you feel ready.
Here's a step by step tutorial on loading textures
http://www.nullterminator.net/gltexture.html
Its important to remember that OpenGL is a state machine, so you have to tell it "I'm going to talk about textures now" that's where the glActiveTexture(); comes in.
Also keep in mind that you will have to load in pixel by pixel the colors from your .jpg (compressed) to your texture array, so either you will need to find a library that will give you bitmap values of your .jpg file or you will need to pre-convert it into a .ppm or a .bmp which will make reading in the values easier.
Related
I'm writing a project using OpenGL, and loading the textures using stb_image.
Some of the textures are loaded flipped upside down (regarding the y-axis) so I use
"stbi flip image vertically on load" to load them properly.
The problem is that some of the textures I load require flipping, and some not,
But of course my code flipps them all.
how can I check (before loading, or at least before flipping) whether or not to flip the
image?
Short answer: always flip when loading an image from stb_image to an OpenGL texture. Longer answer: you can't know whether a user wants to flip the image themselves. As it was posed, I think your question is answered by the question Kai Burjack linked you to (Should I vertically flip the lines of an image loaded with stb_image to use in OpenGL?) because it clarifies the correct use of this feature of stb_image.
If you are going straight from an image file to an OpenGL texture, then you should always flip during import if you want the "up" of the imported texture to match what users see in their art programs. However, if you want to give users the option to load images upside down independent of how the image looks in the art program, you can totally do that, too. The catch is that the user has to tell you. There's no way to know what the user wants, and IMO artists who want their images upside-down are likely to just make them that way in their art programs anyways.
I'm trying to understand cube maps. I have read the following tutorial: https://learnopengl.com/Advanced-OpenGL/Cubemaps My example program is very similar to the tutorial program but I use freeimage for loading textures. My cube map has inverted y view for each face. When I change texture library from stb image to freeimage in the tutorial program I also get inverted y view for each face. Does freeimage use some non-standard convention ? Why I get different results ?
I don't know if there is a standard for this, but I wouldn't say that FreeImage is mirroring the image vertically, it's just the way pixel data is stored.
If you want to read the data with an OpenGL generated texture, you may want to flip the images by code using FreeImage_FlipVertical before FreeImage_GetBits. I guess you are using FreeImage_GetBits to deliver the data to the texture generated in OpenGL, if you are reading the image with scan lines, you can load the data from the bottom up.
Heads-up: If you use multiple formats of images It is likely that you also have other problems regarding the way data is stored, so just to let you know, when you use GetBits and GetScanLine, in the official FreeImage documentation says "It is up to you to interpret these bytes correctly, according to the results of FreeImage_GetBPP, FreeImage_GetRedMask, FreeImage_GetGreenMask and FreeImage_GetBlueMask" so if you have other problems loading the image to OpenGL you may want to check the examples here for interpreting the data:
http://freeimage.sourceforge.net/documentation.html
I am trying to load a texture with non-power-of-two (NPOT) sizes in my application which uses OGLPlus library. So, I use images::Image to load an image as a texture. When I call Context::Bound function to set the texture, it throws an exception. When the size of the input image is POT, it works fine.
I checked the source code of OGLPlus and it seems that it uses glTexImage2D function. I know that I can use gluScaleImage to scale my input image, but it is dated and I want to avoid it. Is there any functions in newer libraries like GLEW or OGLPLUS with the same functionality?
It has been 13 years (OpenGL 2.0) since the restriction of power-of-two on texture sizes was lifted. Just load the texture with glTexImage and, if needed, generate the mipmaps with glGenerateMipmap.
EDIT: If you truly want to scale the image prior to uploading to an OpenGL texture, I can recommend stb_image_resize.h — a one-file public domain library that does that for you.
I have a few questions about using them both. At the moment I have a preexisting renderer I'm trying to use with QT and OpenGL.
A few questions are:
How can I get my results to draw in a QGraphicsScene? Is that even the right output to attempt to be using.
With OpenGL I want to be able to load textures and then be displayed in a window? Do I need to coordinate where to draw the texture or can I just say in the centre of a QWidget?
What paramenter would I usually need, I persume I need a Gluint for the texture, and then parameters for the size?
At the moment my results are quite poor, it seems to render something but basically not either in the correct window or not in the window of choice and basically it seems to 'hide' text e.g. hello, I can only see e. Odd I think.
I'm pretty sure this link will help you code with Qt and OpenGL:
http://wesley.vidiqatch.org/03-08-2009/nehe-opengl-lessons-in-qt-chapter-1-and-2
I used this and the NeHe tutorial to code a small Qt/OpenGL application, so all information you need is contained in both tutorials.
I have these files: sample.obj, sample.mtl and a folder sample containing image jpg. Can somebody give me an example code of opengl texture mapping using above input.
Your problem is not just texture mapping. What you are asking for is loading an Wavefront OBJ model and its material library, then passing this data to OpenGL rendering commands. Depending on how many preexisting code you want (not) to use this takes different amounts of code. However there's no such thing like a simple OpenGL function that does it all in a black box.
Although this is a FAQ and Google brings you some results I didn't find a tutorial that really explains what's going on.
If you want it to be really simple, use a Wavefront loader and render library:
http://www.evl.uic.edu/pape/sw/libwave.html