# OpenGL Mipmaps and FBOs

## Recommended Posts

I am having a hell of a time generating mipmaps for my FBO texture. My mipmaps just aren't being generated properly. I render a grid to the FBO on every frame, and try to generate a full set of mipmaps immediately. Then I draw my FBO texture to the screen: When I move the camera back from the render position, the grid disappears completely within my black quad. Obviously, the renderer is trying to use my mipmaps to render my quad to the screen, but those mipmap texture levels haven't been generated. My FBO texture is 1024x1024. I'm using OpenGL Version 3.2 on an nVidia Quadro 4800 card, Windows 7. Here is my code for creating my FBO:

texData.width = w;
texData.height = h;
texData.bFlipTexture = true;
texData.glType = GL_RGB;

this->autoClear = autoClear;

// create & setup texture
glGenTextures(1, (GLuint *)texData.textureName);   // could be more then one, but for now, just one

glEnable(GL_TEXTURE_2D);

const GLubyte* ver = glGetString(GL_VERSION);
glBindTexture(GL_TEXTURE_2D, (GLuint)texData.textureName[0]);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_REPEAT);//);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_REPEAT);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);		//GL_LINEAR

//glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE); // automatic mipmap - when I include this line and draw my texture
//at a small scale, I see the imagery, but it does not appear to be mipmapped -- it looks like a typical (jagged) linear shrinkage. (See image below)

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB8 , texData.tex_w, texData.tex_h, 0, /*texData.glType*/ GL_RGB, GL_UNSIGNED_BYTE, 0);

// when I use glGenerateMipmapEXT(), I see proper transitions between mipmap levels as I scale down my texture, but every mipmap level
//is just black with no imagery. (See image above.) Level 0 crossfades to black as it reaches a 50% scale.
glGenerateMipmapEXT(GL_TEXTURE_2D);  //Allocate necessary space for mipmaps

glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);

// create & setup FBO
glGenFramebuffersEXT(1, &fbo);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo);

// attach it to the FBO so we can render to it
glFramebufferTexture2DEXT(GL_FRAMEBUFFER_EXT, GL_COLOR_ATTACHMENT0_EXT, GL_TEXTURE_2D, (GLuint)texData.textureName[0], 0);

glGenRenderbuffersEXT(1, &depthBuffer);
glBindRenderbufferEXT(GL_RENDERBUFFER_EXT, depthBuffer);
glRenderbufferStorageEXT(GL_RENDERBUFFER_EXT, GL_DEPTH_COMPONENT, texData.tex_w, texData.tex_h);

// Attach the depth render buffer to the FBO as it's depth attachment
glFramebufferRenderbufferEXT(GL_FRAMEBUFFER_EXT, GL_DEPTH_ATTACHMENT_EXT, GL_RENDERBUFFER_EXT, depthBuffer);

GLenum status = glCheckFramebufferStatusEXT(GL_FRAMEBUFFER_EXT);
if(status != GL_FRAMEBUFFER_COMPLETE_EXT) {
cout<<"glBufferTexture failed to initialize. Perhaps your graphics card doesnt support the framebuffer extension? If you are running osx prior to system 10.5, that could be the cause"<<endl;
std::exit(1);
}


In the code above, you may notice the commented line in which I set: glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE); ...if I use this call instead of glGenerateMipmapEXT(), then I can see my entire FBO texture rendered in my quad, but it is obviously NOT mipmapped: Anyway, when it's time to actually render to my FBO texture, here is my pseudocode:

glBindTexture(GL_TEXTURE_2D, 0);
glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, fbo);

//DRAW to FBO

glBindFramebufferEXT(GL_FRAMEBUFFER_EXT, 0); //unbind the FBO

glBindTexture(GL_TEXTURE_2D, (GLuint)texData.textureName);
//glEnable(GL_TEXTURE_2D); //I'm told I need this on an ATI card, but not necessary for nVidia?
glGenerateMipmapEXT(GL_TEXTURE_2D);


I have tried lots of combinations of tiny tweaks to the different calls, especially glTexImage2D, but haven't gotten anywhere. I've tried to mimic every example usage of glGenerateMipmapEXT() I can find online. I'd rather not deal with gluBuild2DMipmaps(), and I don't know why it should work where these other methods fail. Please help! I've been stuck on this for two days!

##### Share on other sites
Perhaps the 3.2 profile isn't working too well. Can you try it with GL 2 since you are calling glTexEnvf(GL_TEXTURE_ENV, GL_TEXTURE_ENV_MODE, GL_MODULATE);
and using the glGenerateMipmapEXT (the FBO_EXT version)

//glEnable(GL_TEXTURE_2D); //I'm told I need this on an ATI card, but not necessary for nVidia?
That's for regular texture on ATI. For FBO texture, you don't need it even on ATI. Also, it was for really old drivers. Perhaps it is already fixed.

##### Share on other sites
V-man,

Using the 2.0 or 2.1 profile is something I hadn't thought of. I'd love to try, but I have no idea how to do this. I can use glGetString(GL_VERSION) to see which version I'm using, but I can't find a reference online for how to specify an older version/profile. I don't know if it means using a different nVidia driver, gl_.dll, setting preprocessor constants... Where do I start?

##### Share on other sites
Making an old context is done with the old fashion way. Look at any code such as at Nehe. Of course, the version will always say 3.0 even if you have old profile.

##### Share on other sites
You suggested that I try 2.0 because I was using glGenerateMipmapEXT and a lot of other EXT function pointers. I have since updated glee.h and am now using glGenerateMipmap(). Should that make a difference? My results on screen are the same.

I'm using a fairly large code base that does not easily lend itself to being pushed backwards. I don't think that it is worth trying to revert everything to an older version of OpenGL. Is there anything in more recent versions that might work better?

##### Share on other sites
But are you creating a GL 3 context?
Some tutorial here http://www.opengl.org/wiki/Main_Page

## Create an account

Register a new account

• ### Forum Statistics

• Total Topics
628348
• Total Posts
2982207
• ### Similar Content

• Hi all,

I'm starting OpenGL using a tut on the Web. But at this point I would like to know the primitives needed for creating a window using OpenGL. So on Windows and using MS VS 2017, what is the simplest code required to render a window with the title of "First Rectangle", please?

• Hi, New here.
I need some help. My fiance and I like to play this mobile game online that goes by real time. Her and I are always working but when we have free time we like to play this game. We don't always got time throughout the day to Queue Buildings, troops, Upgrades....etc....
I was told to look into DLL Injection and OpenGL/DirectX Hooking. Is this true? Is this what I need to learn?
How do I read the Android files, or modify the files, or get the in-game tags/variables for the game I want?
Any assistance on this would be most appreciated. I been everywhere and seems no one knows or is to lazy to help me out. It would be nice to have assistance for once. I don't know what I need to learn.
So links of topics I need to learn within the comment section would be SOOOOO.....Helpful. Anything to just get me started.
Thanks,
Dejay Hextrix
• By mellinoe
Hi all,
First time poster here, although I've been reading posts here for quite a while. This place has been invaluable for learning graphics programming -- thanks for a great resource!
Right now, I'm working on a graphics abstraction layer for .NET which supports D3D11, Vulkan, and OpenGL at the moment. I have implemented most of my planned features already, and things are working well. Some remaining features that I am planning are Compute Shaders, and some flavor of read-write shader resources. At the moment, my shaders can just get simple read-only access to a uniform (or constant) buffer, a texture, or a sampler. Unfortunately, I'm having a tough time grasping the distinctions between all of the different kinds of read-write resources that are available. In D3D alone, there seem to be 5 or 6 different kinds of resources with similar but different characteristics. On top of that, I get the impression that some of them are more or less "obsoleted" by the newer kinds, and don't have much of a place in modern code. There seem to be a few pivots:
The data source/destination (buffer or texture) Read-write or read-only Structured or unstructured (?) Ordered vs unordered (?) These are just my observations based on a lot of MSDN and OpenGL doc reading. For my library, I'm not interested in exposing every possibility to the user -- just trying to find a good "middle-ground" that can be represented cleanly across API's which is good enough for common scenarios.
Can anyone give a sort of "overview" of the different options, and perhaps compare/contrast the concepts between Direct3D, OpenGL, and Vulkan? I'd also be very interested in hearing how other folks have abstracted these concepts in their libraries.
• By aejt
I recently started getting into graphics programming (2nd try, first try was many years ago) and I'm working on a 3d rendering engine which I hope to be able to make a 3D game with sooner or later. I have plenty of C++ experience, but not a lot when it comes to graphics, and while it's definitely going much better this time, I'm having trouble figuring out how assets are usually handled by engines.
I'm not having trouble with handling the GPU resources, but more so with how the resources should be defined and used in the system (materials, models, etc).
This is my plan now, I've implemented most of it except for the XML parts and factories and those are the ones I'm not sure of at all:
I have these classes:
For GPU resources:
Geometry: holds and manages everything needed to render a geometry: VAO, VBO, EBO. Texture: holds and manages a texture which is loaded into the GPU. Shader: holds and manages a shader which is loaded into the GPU. For assets relying on GPU resources:
Material: holds a shader resource, multiple texture resources, as well as uniform settings. Mesh: holds a geometry and a material. Model: holds multiple meshes, possibly in a tree structure to more easily support skinning later on? For handling GPU resources:
ResourceCache<T>: T can be any resource loaded into the GPU. It owns these resources and only hands out handles to them on request (currently string identifiers are used when requesting handles, but all resources are stored in a vector and each handle only contains resource's index in that vector) Resource<T>: The handles given out from ResourceCache. The handles are reference counted and to get the underlying resource you simply deference like with pointers (*handle).
And my plan is to define everything into these XML documents to abstract away files:
Resources.xml for ref-counted GPU resources (geometry, shaders, textures) Resources are assigned names/ids and resource files, and possibly some attributes (what vertex attributes does this geometry have? what vertex attributes does this shader expect? what uniforms does this shader use? and so on) Are reference counted using ResourceCache<T> Assets.xml for assets using the GPU resources (materials, meshes, models) Assets are not reference counted, but they hold handles to ref-counted resources. References the resources defined in Resources.xml by names/ids. The XMLs are loaded into some structure in memory which is then used for loading the resources/assets using factory classes:
Factory classes for resources:
For example, a texture factory could contain the texture definitions from the XML containing data about textures in the game, as well as a cache containing all loaded textures. This means it has mappings from each name/id to a file and when asked to load a texture with a name/id, it can look up its path and use a "BinaryLoader" to either load the file and create the resource directly, or asynchronously load the file's data into a queue which then can be read from later to create the resources synchronously in the GL context. These factories only return handles.
Factory classes for assets:
Much like for resources, these classes contain the definitions for the assets they can load. For example, with the definition the MaterialFactory will know which shader, textures and possibly uniform a certain material has, and with the help of TextureFactory and ShaderFactory, it can retrieve handles to the resources it needs (Shader + Textures), setup itself from XML data (uniform values), and return a created instance of requested material. These factories return actual instances, not handles (but the instances contain handles).

Is this a good or commonly used approach? Is this going to bite me in the ass later on? Are there other more preferable approaches? Is this outside of the scope of a 3d renderer and should be on the engine side? I'd love to receive and kind of advice or suggestions!
Thanks!
• By nedondev
I 'm learning how to create game by using opengl with c/c++ coding, so here is my fist game. In video description also have game contain in Dropbox. May be I will make it better in future.
Thanks.

• 10
• 9
• 24
• 11
• 9