• Advertisement
Sign in to follow this  

OpenGL Struggling with textures in openGL

Recommended Posts

Hi,

I am trying to define my own texture but struggling to get even a simple test to work. I have been hitting my head against the wall all day unable to move past this issue (I am sure you remember the feeling) so any help would be gratefully appreciated.

-> I am just seeing a black box where the texture colour should be (in this simple test I am just expecting a white box in the middle of the screen)

->There is no error from glGetError() and the shader compiles and links without giving an error.

->In the fragment shader if I comment out the texture line and instead just return a vec4  then it will display a solid colour with no problem

I have posted the essential elements of the code below. Can anyone spot what I am missing?
 

//Position vertices and texture coordinates for a box
GLfloat screen2DVertices[] = 
{ //x, y, z                    //u, v
-0.8f, -0.8f, 0.0f,        0.0f, 0.0f, // bottom left corner
-0.8f,  0.8f, 0.0f,        0.0f, 1.0f, // top left corner
0.8f,  0.8f, 0.0f,         1.0f, 1.0f, // top right corner
0.8f, -0.8f, 0.0f,         1.0f, 0.0f, // bottom right corner
};

GLushort screen2DIndices[] = 
{ 
0,1,2, // first triangle (bottom left - top left - top right)
0,2,3  // second triangle (bottom left - top right - bottom right)
};

//Texture width in pixels
const int TEXTURE_WIDTH = 32;
const int TEXTURE_HEIGHT = 32;

//3 RGB values per pixel
float texturePixels[TEXTURE_WIDTH * TEXTURE_HEIGHT * 3];

//Test with all white r = g = b = 1.0f
for (int i = 0; i < TEXTURE_WIDTH * TEXTURE_HEIGHT * 3; i++)
{
texturePixels[i] = 1.0f;
}

GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);


// Load texture
GLuint tex;
glGenTextures(1, &tex);
glBindTexture(GL_TEXTURE_2D, tex);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGB, TEXTURE_WIDTH, TEXTURE_HEIGHT, 0, GL_RGB, GL_FLOAT, texturePixels);

GLuint vbo;
glGenBuffers(1, &vbo);

// Create an element array
GLuint ebo;
glGenBuffers(1, &ebo);

glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, sizeof(screen2DVertices), screen2DVertices, GL_STATIC_DRAW);

glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(screen2DIndices), screen2DIndices, GL_STATIC_DRAW);


// Specify the layout of the vertex data
GLint posAttrib = glGetAttribLocation(screenShader.Program, "position");
glEnableVertexAttribArray(posAttrib);
glVertexAttribPointer(posAttrib, 3, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (void*)0);

GLint texAttrib = glGetAttribLocation(screenShader.Program, "texcoord");
glEnableVertexAttribArray(texAttrib);
glVertexAttribPointer(texAttrib, 2, GL_FLOAT, GL_FALSE, 5 * sizeof(GLfloat), (void*)(3 * sizeof(GLfloat)));

while (!glfwWindowShouldClose(window))
{
glfwPollEvents();

glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
glClear(GL_COLOR_BUFFER_BIT);

screenShader.Use();
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, (void*)0);

glfwSwapBuffers(window);
}

Shaders:


//---------------------------Vertex Shader------------------------------------------
#version 330 core

in vec3 position;
in vec2 texcoord;

out vec2 Texcoord;

void main()
{
Texcoord = texcoord;
gl_Position = vec4(position, 1.0);
}

//---------------------------Fragment Shader------------------------------------------
#version 330 core

in vec2 Texcoord;
out vec4 outColour;
uniform sampler2D tex;

void main()
{
outColour = texture(tex, Texcoord) * vec4(1.0f);
}
Edited by Promit

Share this post


Link to post
Share on other sites
Advertisement

How does this work at all with (void*)0?

glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_SHORT, (void*)0);

The program is expecting a 24 bit image so check that.

Share this post


Link to post
Share on other sites

The glDrawElements calls are in no way related to texture as one can draw untextured primitives. However, I am not seeing in the code you posted, how you are notifying the fragment shader as to which texture unit, the sampler's texture is in. Hate to be sarcastic here, but it does not magically appear in the shader because you created one and bind it. Usually, you use glUniform1i, specify the attribute location ( of the sampler ) retrieved from the compile program or specified in the shader  along with the texture/sampler unit the texture was bound to.

Share this post


Link to post
Share on other sites

Few hints:

 

If the rendering is all black, that generally means that the texture has not been correctly created or used (does glIsTexture gives the right result ?)

If the rendering has some color which looks like a color from the image (some kind of red if the image is redish for example), then the issue is most certainly related to texture coordinates.

 

Also try to change the underlying type the texture uses. Use GL_UNSIGNED_BYTE for start. Try also to use a different internal format. GL_RGB8 would do the thing.

Share this post


Link to post
Share on other sites

Also a very common gotcha for this is mipmaps. If you upload the texture but don't create mipmaps, and it samples from the blank mipmaps you just get black.

Share this post


Link to post
Share on other sites

Thank you all so much for the suggestions, it is REALLY appreciated! lawnjelly you are my saviour, I added mipmaps and immediately got a white square (they were not part of the tutorial that I was using as a reference so I didn't realise they were so important). cgrant I thought that you had found the problem but strangely it works even without sending the uniform location, not sure why.

Thanks again to everyone!

Share this post


Link to post
Share on other sites

You want to make sure the first time you bind a texture at creation that you setup the glTexParameter  calls that describe your sampling types for minification and magnification such as anisotropic filtering or simple point sampling.

Share this post


Link to post
Share on other sites

Also changing the value of glClearColor to anything but black lets you know if there is any rendering direction ahead of you at least.

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

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