OpenGL not rendering textures

Question

i'm using OpenGL 2.1 with SDL2.0 and i'm trying to render a texture, using this steps: load the image:

    Image* image = new Image();

image->image = SDL_LoadBMP(path.c_str());

if (!image->image)
    throw std::runtime_error(SDL_GetError());

return image;

and then generate a texture for it:

Texture2D* Texture2D::fromImage(const Image* image){
GLint format;
Texture2D* t2d = new Texture2D();

glGenTextures(1, &t2d->tid);
glBindTexture(GL_TEXTURE_2D, t2d->tid);
t2d->size.setWidth(image->getWidth());
t2d->size.setHeigth(image->getHeight());

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);

switch (image->getBPP()){
case 24:
    format = GL_RGB;
    break;
case 32:
    format = GL_RGBA;
    break;
default:
    throw std::runtime_error("Unsurpoted pixel format!");
    break;
}

glTexImage2D(GL_TEXTURE_2D, 0, format, image->getWidth(), image->getHeight(), 0, format, GL_UNSIGNED_BYTE, image->getPixels());

return t2d;
}

and then i try to render it:

void Painter::drawTexture(Texture2D* texture, const SizeF& size, const PointF& position){
camera.set(camera.getWidth(), camera.getHeight());

texture->bind();//only call glBindTexture(GL_TEXTURE_2D, tid);

glBegin(GL_QUADS);
glColor4f(color.getR(), color.getG(), color.getB(), color.getA());
glTexCoord2f(0.0f, 1.0f);
glVertex2f(position.getX(), position.getY());
glTexCoord2f(1.0f, 1.0f);
glVertex2f(position.getX() + size.getWidth(), position.getY());
glTexCoord2f(1.0f, 0.0f);
glVertex2f(position.getX() + size.getWidth(), position.getY() + size.getHeight());
glTexCoord2f(0.0f, 0.0f);
glVertex2f(position.getX(), position.getY() + size.getHeight());
glEnd();
}

but all i got is box with the defined color, i don't understand why, i have already followed this steps before to render a texture, but this time it is not working, i'm not using glEnable(GL_TEXTURE_2D) because i read that this is not necessary, but when i do call it i got the error code 1282, but i got no errors on the textures creation, can someone give me some light here? thanks

Answer 1

Explicitly enabling texture samplers is not necessary if you're drawing using the programmable shader pipeline (since whether or not you're sampling from textures, and what type of sampling to do across those textures is explicit in the shader code that you're using)

However, based upon your code sample you appear to be rendering using the fixed function pipeline, in which case you do need to explicitly enable (and disable) each texture sampler that you plan to use, to tell the fixed function pipeline what you expect it to do.

So you want to do something like this, in this order:

glActiveTexture(GL_TEXTURE0);      // Hey OpenGL, we're about to give commands for texture sampler 0.
glBindTexture(GL_TEXTURE_2D, tid); // when the currently-active sampler samples from a 2D texture, this is the texture to use.
glEnable(GL_TEXTURE_2D);           // the currently-active sampler should actually use the bound 2D texture.
//
// -- draw stuff here
//
glDisable(GL_TEXTURE_2D);          // disable currently-active sampler's 2D sampling again, so it doesn't affect any future draw calls.