OpenGL ES 2.0 texturing

Question

I'm trying to render a simple textured quad in OpenGL ES 2.0 on an iPhone. The geometry is fine and I get the expected quad if I use a solid color in my shader:

gl_FragColor = vec4 (1.0, 0.0, 0.0, 1.0);

And I get the expected gradients if I render the texture coordinates directly:

gl_FragColor = vec4 (texCoord.x, texCoord.y, 0.0, 1.0);

The image data is loaded from a UIImage, scaled to fit within 1024x1024, and loaded into a texture like so:

glGenTextures (1, &_texture);
glBindTexture (GL_TEXTURE_2D, _texture);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA, 
    GL_UNSIGNED_BYTE, data);

width, height, and the contents of data are all correct, as examined in the debugger.

When I change my fragment shader to use the texture:

gl_FragColor = texture2D (tex, texCoord);

... and bind the texture and render like so:

glActiveTexture (GL_TEXTURE0);
glBindTexture (GL_TEXTURE_2D, _texture);

// this is unnecessary, as it defaults to 0, but for completeness...
GLuint texLoc = glGetUniformLocation(_program, "tex");          
glUniform1i(texLoc, 0);

glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

... I get nothing. A black quad. glGetError() doesn't return an error and glIsTexture(_texture) returns true.

What am I doing wrong here? I've been over and over every example I could find online, but everybody is doing it exactly as I am, and the debugger shows my parameters to the various GL functions are what I expect them to be.

Answer 1

After glTexImage2D, set the MIN/MAG filters with glTexParameter, the defaults use mipmaps so the texture is incomplete with that code.