• Advertisement
Sign in to follow this  

OpenGL diff btw glTexCoord2i and glTexCoord2f

This topic is 3727 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

If you intended to correct an error in the post then please contact us.

Recommended Posts

I am playing with texturing in OpenGL and I have bumped into something I don't understand concerning texture coordinates: I have a 512x512 texture and thought both codes would behave in the same way :
//int size = something;
glTexCoord2i(0, 0);     glVertex2i(0, 0);
glTexCoord2i(0, 511);   glVertex2i(0, size);
glTexCoord2i(511, 511); glVertex2i(size, size);
glTexCoord2i(511, 0);   glVertex2i(size, 0);

//int size = something;
glTexCoord2f(0, 0);     glVertex2i(0, 0);
glTexCoord2f(0, 1);     glVertex2i(0, size);
glTexCoord2f(1, 1);     glVertex2i(size, size);
glTexCoord2f(1, 0);     glVertex2i(size, 0);

But they don't. The code using glTexCoord2f gives me what I want, but the code using glTexCoord2i gives very strange results, where the texture appears to be totally messed up depending on size's value.

Share this post


Link to post
Share on other sites
Advertisement
The two functions behave the exact same way, by setting texture coordinates. Your use of glTexCoord2i attempts to set texels. So, glTexCoord2i(1, 1), will give you the results you're after.

The docs don't make any distinction between them, apart from parameter types.

Share this post


Link to post
Share on other sites
The entry in the blue book for glTexCoord doesn't say anything about how integer values are interpreted, helpfully. (http://glprogramming.com/blue/ch05.html#id5535535)

The red book has this to say:

"Note that integer texture coordinates are interpreted directly rather than being mapped to the range [-1,1] as normal coordinates are." (http://glprogramming.com/red/chapter09.html#name6)

So they're interpreted directly, but with reference to what? I *think* that this means maybe you should be using 0 and 1 for the int code, same as for the float code. Although this would mean you can't use ints for accurate positioning. :o

Have you tried using your (int) size, or maybe size-1, as the non-zero argument to the int version? (Assuming size is something other than 512, which you've already tried...) Maybe they mean "interpreted directly in world units"...?

This has puzzled me too, but I hadn't gotten around to investigating yet.

Share this post


Link to post
Share on other sites
Yes I find the documentation on the subject very light (The blue book is a real joke).
I have even taken a look at the opengl specifications but haven't found anything interesting.

I really wonder how one is supposed to reference texture coordinates with pixel precision. I understand the purpose of glTexCoord2f with the [0.0 ; 1.0] coordinate system (which by the way is different from what the red book says when talking about [-1; 1] mapping), but when dealing with simple 2D blits this approach doesn't look like the most simple one.

PS : The only purpose of my size variable is to draw quads of different sizes, but I wouldn't expect it to have any influence on the texture coordinates. Although it clearly has when using glTexCoord2i.

Share this post


Link to post
Share on other sites
glTexCoord2i() is for INTEGER values, and

glTexCoord2f() is for floating point values.

if you are only using 1,2,3,4,5, ect... then integer is fine, but if you need to use the fractional part of a whole number you need to use glTexCoord2f()

Hope this clears this up.

Share this post


Link to post
Share on other sites
What I am looking for is something describing the texture coordinate system when using integers.
When using floats the system ranges from coordinate (0.0, 0.0) to coordinate (1.0, 1.0).

But I have strong doubts that this is the same with integers. Instead I would have expected the system to range from coordinate (0, 0) to coordinate (texture_size - 1, texture_size - 1). But when doing some tests this assumption appears to be wrong. Else my 1st piece of code would behave like my 2nd one, but this is not the case.

Share this post


Link to post
Share on other sites
No matter what function you use, the texture coordinates are specified in normalized coordinates; integers or not. That means you're tiling the texture 511 times in your example. However...

glMatrixMode(GL_TEXTURE);
glLoadIdentity();
glScalef(1/texture_width, 1/texture_height, 1);

Now you can reference the texture with texel coordinates instead, as they will be scaled to proper normalized coordinates automatically. Also, keep in mind that the full texture is referenced in the range [0, texture_width/height], not [0, texture_width/height-1].

Share this post


Link to post
Share on other sites
Thanks Brother Bob, this makes sense.
And concerning "[0, texture_width/height], not [0, texture_width/height-1]", this was also tickling me, as else it wouldn't have been coherent with [0.0, 1.0].

From what I understand it seems that directly using normalized float coordinates is more natural than bothering with integers.

Share this post


Link to post
Share on other sites
Sign in to follow this  

  • Advertisement
  • Advertisement
  • Popular Tags

  • Advertisement
  • Popular Now

  • Similar Content

    • By LifeArtist
      Good Evening,
      I want to make a 2D game which involves displaying some debug information. Especially for collision, enemy sights and so on ...
      First of I was thinking about all those shapes which I need will need for debugging purposes: circles, rectangles, lines, polygons.
      I am really stucked right now because of the fundamental question:
      Where do I store my vertices positions for each line (object)? Currently I am not using a model matrix because I am using orthographic projection and set the final position within the VBO. That means that if I add a new line I would have to expand the "points" array and re-upload (recall glBufferData) it every time. The other method would be to use a model matrix and a fixed vbo for a line but it would be also messy to exactly create a line from (0,0) to (100,20) calculating the rotation and scale to make it fit.
      If I proceed with option 1 "updating the array each frame" I was thinking of having 4 draw calls every frame for the lines vao, polygons vao and so on. 
      In addition to that I am planning to use some sort of ECS based architecture. So the other question would be:
      Should I treat those debug objects as entities/components?
      For me it would make sense to treat them as entities but that's creates a new issue with the previous array approach because it would have for example a transform and render component. A special render component for debug objects (no texture etc) ... For me the transform component is also just a matrix but how would I then define a line?
      Treating them as components would'nt be a good idea in my eyes because then I would always need an entity. Well entity is just an id !? So maybe its a component?
      Regards,
      LifeArtist
    • By QQemka
      Hello. I am coding a small thingy in my spare time. All i want to achieve is to load a heightmap (as the lowest possible walking terrain), some static meshes (elements of the environment) and a dynamic character (meaning i can move, collide with heightmap/static meshes and hold a varying item in a hand ). Got a bunch of questions, or rather problems i can't find solution to myself. Nearly all are deal with graphics/gpu, not the coding part. My c++ is on high enough level.
      Let's go:
      Heightmap - i obviously want it to be textured, size is hardcoded to 256x256 squares. I can't have one huge texture stretched over entire terrain cause every pixel would be enormous. Thats why i decided to use 2 specified textures. First will be a tileset consisting of 16 square tiles (u v range from 0 to 0.25 for first tile and so on) and second a 256x256 buffer with 0-15 value representing index of the tile from tileset for every heigtmap square. Problem is, how do i blend the edges nicely and make some computationally cheap changes so its not obvious there are only 16 tiles? Is it possible to generate such terrain with some existing program?
      Collisions - i want to use bounding sphere and aabb. But should i store them for a model or entity instance? Meaning i have 20 same trees spawned using the same tree model, but every entity got its own transformation (position, scale etc). Storing collision component per instance grats faster access + is precalculated and transformed (takes additional memory, but who cares?), so i stick with this, right? What should i do if object is dynamically rotated? The aabb is no longer aligned and calculating per vertex min/max everytime object rotates/scales is pretty expensive, right?
      Drawing aabb - problem similar to above (storing aabb data per instance or model). This time in my opinion per model is enough since every instance also does not have own vertex buffer but uses the shared one (so 20 trees share reference to one tree model). So rendering aabb is about taking the model's aabb, transforming with instance matrix and voila. What about aabb vertex buffer (this is more of a cosmetic question, just curious, bumped onto it in time of writing this). Is it better to make it as 8 points and index buffer (12 lines), or only 2 vertices with min/max x/y/z and having the shaders dynamically generate 6 other vertices and draw the box? Or maybe there should be just ONE 1x1x1 cube box template moved/scaled per entity?
      What if one model got a diffuse texture and a normal map, and other has only diffuse? Should i pass some bool flag to shader with that info, or just assume that my game supports only diffuse maps without fancy stuff?
      There were several more but i forgot/solved them at time of writing
      Thanks in advance
    • By RenanRR
      Hi All,
      I'm reading the tutorials from learnOpengl site (nice site) and I'm having a question on the camera (https://learnopengl.com/Getting-started/Camera).
      I always saw the camera being manipulated with the lookat, but in tutorial I saw the camera being changed through the MVP arrays, which do not seem to be camera, but rather the scene that changes:
      Vertex Shader:
      #version 330 core layout (location = 0) in vec3 aPos; layout (location = 1) in vec2 aTexCoord; out vec2 TexCoord; uniform mat4 model; uniform mat4 view; uniform mat4 projection; void main() { gl_Position = projection * view * model * vec4(aPos, 1.0f); TexCoord = vec2(aTexCoord.x, aTexCoord.y); } then, the matrix manipulated:
      ..... glm::mat4 projection = glm::perspective(glm::radians(fov), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f); ourShader.setMat4("projection", projection); .... glm::mat4 view = glm::lookAt(cameraPos, cameraPos + cameraFront, cameraUp); ourShader.setMat4("view", view); .... model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f)); ourShader.setMat4("model", model);  
      So, some doubts:
      - Why use it like that?
      - Is it okay to manipulate the camera that way?
      -in this way, are not the vertex's positions that changes instead of the camera?
      - I need to pass MVP to all shaders of object in my scenes ?
       
      What it seems, is that the camera stands still and the scenery that changes...
      it's right?
       
       
      Thank you
       
    • By dpadam450
      Sampling a floating point texture where the alpha channel holds 4-bytes of packed data into the float. I don't know how to cast the raw memory to treat it as an integer so I can perform bit-shifting operations.

      int rgbValue = int(textureSample.w);//4 bytes of data packed as color
      // algorithm might not be correct and endianness might need switching.
      vec3 extractedData = vec3(  rgbValue & 0xFF000000,  (rgbValue << 8) & 0xFF000000, (rgbValue << 16) & 0xFF000000);
      extractedData /= 255.0f;
    • By Devashish Khandelwal
      While writing a simple renderer using OpenGL, I faced an issue with the glGetUniformLocation function. For some reason, the location is coming to be -1.
      Anyone has any idea .. what should I do?
  • Advertisement