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[1.12.2] OpenGL Guidance


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I'm trying to change a model's texture at runtime, several times (when the user right clicks with certain items). I would specifically like to edit certain pixels on the texture and display that. I have been scouring the web for people who've done this and have not had much luck finding working solutions. I have gathered that I will most likely need to use OpenGL as mentioned in a few other threads. As far as I can tell GlStateManager doesn't have much documentation and I can't figure out whether to use things like GL11.GL_RGBA8 or GL12.GL_BGRA for various parameters. 


I have a few problems, namely that the model loaded from circle.json doesn't actually change from the texture specified there (maybe I'm not supposed to include a circle.json at all?), and also that I don't know what any of the OpenGL parameters are. I would mainly like to understand those better and also figure out how to tell which GL11 and GL12 stuff to use (so that if I want to update the mod in the future I can make sure they're the right parameters..


Also, I do not know the correct order for doing things with OpenGL. My understanding is that you bind the texture with one of the many bindTexture() functions, some of them using ResourceLocations and others using mysterious constants (



, then you use glGetTexImage to load the image to an IntBuffer, then you modify the int buffer, and send it back with glTexImage2D. Do you bind it again? I was able to run this code without issue, but the model didn't change in game and OpenGL was spamming some surprisingly non-crashing "invalid enum" errors, which I assume had to do with my incorrect parameter use.


Here's some code (may be slightly off because I commented stuff out to try rewriting it based on MapItemRenderer to no avail):


    public void doRender(CircleTileEntity circle) {

        UnorderedList catalysts = circle.getCatalysts();
        if (catalysts == null) catalysts = new UnorderedList();
        ArrayList<String> order = catalysts.getOrder();
        if (order == null) order = new ArrayList();
        CircleData displayMe;
        if (loadedCircle.containsKey(order)) {
            displayMe = loadedCircle.get(order); // found a matching map
        } else {
            IntBuffer colorBuf = BufferUtils.createIntBuffer(PIXEL_COUNT);
            //create a map and save it
            CircleData image = new CircleData();
            GlStateManager.glGetTexImage(GL11.GL_TEXTURE_2D, 0, GL12.GL_BGRA, GL12.GL_UNSIGNED_INT_8_8_8_8_REV, colorBuf);
            displayMe = image;
            loadedCircle.put(order, displayMe);
            IntBuffer imageOut = BufferUtils.createIntBuffer(PIXEL_COUNT * 4);
            for(int x = 0; x < PIXEL_COUNT; x++) {
                int pixel = displayMe.colors[x];
            displayMe.imageOut = imageOut;
        GlStateManager.glTexImage2D(GL11.GL_TEXTURE_2D, 0, GL12.GL_BGRA, SIDE_SIZE, SIDE_SIZE,
                0, GL12.GL_BGRA, GL12.GL_UNSIGNED_INT_8_8_8_8_REV, displayMe.imageOut);


I appreciate any advice anyone has or if anyone has a link to read about these OpenGL functions and parameters.

Edited by stepsword
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I ended up figuring it out if anyone's interested. Based on my tests it seemed like I was successfully pulling the image with glGetTexImage() and also successfully loading the modified image (ended up switching to using MapItemRenderer's DynamicTexture in the process, but I think could have gotten it working without that, since the Dynamic Texture just uses glTexSubImage2D()  - and even specifies the correct parameters!!), but I didn't know you had to actually go and draw the loaded image with a Tessellator. I thought the loading was enough to swap out the textures.


I did originally try to use MapItemRenderer's Tessellator code just to see if it could render something, but since the position was wrong I didn't see any changes to my block and assumed something else was broken.


So! It's rendering now, albeit in the wrong part of the block, but at least I have a rough idea of how to fix it since I can see it rendering now.

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