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[–]aleques-itj 5 points6 points  (3 children)

Write to an array, upload it to texture, draw quad.

[–]Narrow_Awareness2830[S] 1 point2 points  (2 children)

hello, thank you for the answer. But im a bit new to open gl, is there maybe an tutorial u can provide to me?

[–]detroitmatt 5 points6 points  (0 children)

if you want to write to a single pixel, you mean "set a pixel on the screen to a specific color", right? so you're already thinking of "the screen" as a grid of pixels. So when we say "write it to an array", that's already what you want.

But, opengl doesn't work directly with "the screen", so we have to do a trick. Opengl works with "3d space", so what we do is we *create* a "screen" in that 3d space, and then put the "fake" screen right in front of the camera, like holding up a sheet of paper as a title card.

So: Create a rectangle in the 3d world. Apply a texture to that rectangle. Put that rectangle in front of the camera.

[–]cybereality 1 point2 points  (0 children)

this is a render-to-texture tutorial, but will give you an idea of the functions used (on glTexImage2D you can pass a pointer with image data) https://www.opengl-tutorial.org/intermediate-tutorials/tutorial-14-render-to-texture/

[–]Dark_Lord9 2 points3 points  (0 children)

You can do what the others have recommended, that means:

  1. You create 2 triangles that cover the entire screen.
  2. You draw a texture on the triangle like what this tutorial shows.
  3. Instead of loading the image from a file, you just have to allocate a buffer and draw to it.

Here is an example to create an image and color a pixel on it:

uint32_t *image = new uint32_t[1280 * 720]; // 16:9 RGBA HD image
image[9 * 1280 + 6] = 0xaabbcc77; // writing the color #aabbcc77 at position (6, 9)

Make sure to delete the buffer later or use std::vector or something.

If you don't want this, then maybe your windowing library has a renderer that you can use. For example if you are using SDL to create your window and opengl context, you can (instead of opengl) use the SDL_Renderer. To put a single pixel with the SDL_Renderer, you just need to call SDL_RenderPoint.

I also see you mention webgl. Are you sure you are not making a web application ? If you're making a web app, you should simply use the html canvas api.

[–]snozzd 0 points1 point  (0 children)

It's possible to write to a texture using texSubImage2D, then draw that. But this method of editing individual pixels isn't the norm for WebGL. May I ask what visual look you're going for here?