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Modifying a texture

Started by Enjoy Mar 2, 2008 at 9:29 AM 3 replies 2.5k views

Original Post

Mar 2, 2008 at 9:29 AM

Hello, I am loading texture from TGA file. How can I modify a loaded texture? And how can I generate a texture on my own? For example if I want to generate a cloud texture and after this to attach this to a billboard. I am storing Image data like this: unsigned char *data Thank you in advance.

Trenki

Mar 2, 2008 at 9:39 AM

To generate a texture on your own simply allocate the required amount of memory and write the pixel data to the allocated pixels.
You can modify an already uploaded OpenGL texture with glTexSubImage.

polymorphed

Mar 2, 2008 at 9:53 AM

Assuming that your .TGA loader loads the image into a bitmap array in the RGB (or RGBA) format, it should be as easy as just changing the colors yourself:

unsigned char* image;image[0] = Red of #1 pixelimage[1] = Green of #1pixelimage[2] = Blue of #1 pixelimage[3] = Alpha of #1 pixelimage[4] = Red of #2 pixelimage[5] = Green of #2pixelimage[6] = Blue of #2 pixelimage[7] = Alpha of #2 pixelimage[8] = Red of #3 pixel// Etc..

And generating your own texture is just as easy

int width = 256;int height = 256;int format = 3; // 3 bytes per pixel, RGBunsigned char* texture = new unsigned char[width*height*format];for (int x = 0; x < width; x++){    for (int y = 0; y < height; y++)    {        texture[((y*width) + x)*format]   = Red;        texture[((y*width) + x)*format+1] = Green;        texture[((y*width) + x)*format+2] = Blue;    }}glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGB, GL_UNSIGNED_BYTE, texture);

I hope this helps.

Lord_Evil

Mar 2, 2008 at 11:21 AM

Like polymorphed showed, modifying a texture when loading it is as easy as changing individual pixels. This way you can also generate textures - the only thing you need is some algorithm for generating procedural textures.

Updating a texture that is loaded to video memory can be done via glTexSubImage2D. This function let's you update a rectangular region of the texture with new data.

Enjoy

Author

Enjoy

Mar 2, 2008 at 12:56 PM

Many thanks,
I just didn't know how to write pixel data.

I will try if it is working for me.

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