Glubyte array opengl

OpenGL
1

I want to load a texture and fill several arrays with texture data. I mean to load the image and maybe use glTexSubImage2D() to copy tiles from a loaded .bmp file into Glubyte arrays. Im not sure how to do this, what is the syntax for doing this? A tile is 14 pixels by 14 pixels and the large image will contain these tiles. How do you fill the Glubyte array?

2

glTexSubImage2D copies data from client memory into an existing texture. glGetTexImage copies the data from an existing texture into client memory. glGetTextureSubImage (requires OpenGL 4.5 or the ARB_get_texture_sub_image extension) copies a rectangle from an existing texture into client memory.

If you’re copying from client memory to client memory, that isn’t something OpenGL deals with.

3

The large file is loaded into a texture unit. Like its going to be used but its an atlas, which function can be used to copy the data into a array of glubyte or gluint. The array is like this.

    //define colors for simplicity
    #define White {0x00, 0x00, 0x00}
    #define Black {0xff, 0xff, 0xff}
    #define Red {0xff, 0x00, 0x00}
    #define Blue {0x00, 0x00, 0xff}
    //Create a texture
    GLubyte ExampleWall[][3] = 
    {
        Black, White,
        Blue, Red,
    };

I want to update this 2x2 texture array to hold 14 texels by 14 texels that is a piece of a large loaded texture file.

4

Im guessing you will have to copy the contents using

glReadPixels( x, y, width, height, GL_RGB , type);

Im not sure which type to select for the loaded texture but theres trial and error.

//LoadFromTextureAtlas Function

void LFTA(int LFTAStartX, LFTAStartY, int LFTAWidth, int LFTAHeight)            
    int num_components = 3; // For RGB
    GLubyte* LFTAPixelData = new GLubyte[width * height * num_components];
    glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, LFTAPixelData);

How do I make a function so I can load the data into texture arrays like the one I posted above? The array needs to be updated with the atlas information. I want

GLubyte ExampleWall[][3] = LFTA(0,14,14,14)

This call to LFTA should update or make a array in the programs ram so there can be as many textures as the ram can hold. Since its a GLubyte array it can be loaded using

glTexImage2D(GL_TEXTURE_2D, 0, 3, 14, 14, 0, GL_RGB, GL_UNSIGNED_BYTE, ExampleWall);
5

How do I make a function that makes a array named in the function call so it can be used with a string to name the new texture array.

For example

LFTA("NewTextureName",0,14,14,14);

This will make a new GLubyte array named NewTextureName that has 14 by 14 texels. It is offset 14 pixels into the image like it has skipped a tile of the same size.

//LoadFromTextureAtlas Function

void LFTA(???, int LFTAStartX, LFTAStartY, int LFTAWidth, int LFTAHeight)            
    int num_components = 3; //3 For RGB
    GLubyte* LFTAPixelData = new GLubyte[width * height * num_components];
    glReadPixels(0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, LFTAPixelData);

The following is from an example

//Declare a 3D array to hold the pixel data
GLubyte pixels[w][h][3];
//Read pixels from the framebuffer into the array
glReadPixels(0, 0, w, h, GL_RGB, GL_UNSIGNED_BYTE, pixels);

I just need it in a function where I name the array by adding a name as a string to the function that doesnt have spaces.