Binding multiple textures OpenGL to different quads

Question

I've managed to get my game to read in a PNG file, and successfully texture my objects. To be honest, I can't 100% nail down how it's actually working - and now I'd like to extend it to loading several textures, and using the one I specify.

Here's my PNG loading function:

//Loads PNG to texture
GLuint loadPNG(string name) {
    nv::Image img;
    GLuint myTextureID;

    if (img.loadImageFromFile(name.c_str())) {
        glGenTextures(1, &myTextureID);
        glBindTexture(GL_TEXTURE_2D, myTextureID);
        glTexParameteri(GL_TEXTURE_2D, GL_GENERATE_MIPMAP, GL_TRUE);
        glTexImage2D(GL_TEXTURE_2D, 0, img.getInternalFormat(), img.getWidth(), img.getHeight(), 0, img.getFormat(), img.getType(), img.getLevel(0));
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
        glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
        glTexParameterf(GL_TEXTURE_2D, GL_TEXTURE_MAX_ANISOTROPY_EXT, 16.0f);
    }
    else {
        MessageBox(NULL, L"Failed to load texture", L"Sorry!", MB_OK | MB_ICONINFORMATION);
    }
    return myTextureID;
}

In my main function, I define the texture like this:

//Load in player texture
testTexture = loadPNG("test.png");

where testTexture is a global variable, of type GLuint. And drawing my rectangles in my main draw loop is done this way:

//Used to draw rectangles
void drawRect(gameObject &p) {
    glEnable(GL_TEXTURE_2D);

    //Sets PNG transparent background
    glEnable(GL_BLEND);

    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
    //glBindTexture(GL_TEXTURE_2D, myTexture);
    glBegin(GL_QUADS);
    glTexCoord2f(0.0, 0.0); glVertex2f(p.x, p.y);
    glTexCoord2f(1.0, 0.0); glVertex2f(p.x + p.width, p.y);
    glTexCoord2f(1.0, 1.0); glVertex2f(p.x + p.width, p.y + p.height);
    glTexCoord2f(0.0, 1.0); glVertex2f(p.x, p.y + p.height);
    glEnd();

    glDisable(GL_TEXTURE_2D);
}

This works fine, texturing all my objects with the defined texture. However, I'd like to be able to define more textures, and use those. I tried moving:

glBindTexture(GL_TEXTURE_2D, myTextureID);

from the loadPNG function, into my drawRect, as:

glBindTexture(GL_TEXTURE_2D, testTexture);

However this doesn't apply any texture whatsoever. If anyone has any ideas, I'd really appreciate the help. Thanks!

When you moved glBindTexture(GL_TEXTURE_2D, myTextureID);, did you delete it from loadPNG? — Indiana Kernick
– Indiana Kernick, Commented Apr 21, 2019 at 9:54

Sneaky Turtle · Accepted Answer · 2019-04-21 10:00:50Z

4

You have to bind the texture in order to initialize it with glTexImage2D. Don't remove the call to glBindTexture from loadPNG. If you want to render with a different texture, simply bind the texture before rendering the quads.

answered Apr 21, 2019 at 10:00

Sneaky Turtle

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6 Comments

eddiewastaken Over a year ago

Just tried this, still no texture! I added glBindTexture(GL_TEXTURE_2D, testTexture2); before (and also tried it after) glEnable(GL_TEXTURE_2D); inside drawRect.

eddiewastaken Over a year ago

Should glTexImage2D be moved to drawRect?

Indiana Kernick Over a year ago

@eddiewastaken What about loadPNG? Are you binding the texture in there? You need to bind the texture to initialise it.

Indiana Kernick Over a year ago

@eddiewastaken Keep glTexImage2D in loadPNG

eddiewastaken Over a year ago

Yes, the only change I made from the original code is adding glBindTexture(GL_TEXTURE_2D, testTexture2); to drawRect

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