OpenGL ES 2.0 texturing - iphone

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.

Answer 2

I was experiencing the same issue (black quad) and could not find an answer until a response by jfcalvo from this question led me to the cause. Basically make sure you are not loading the texture in a different thread.

Answer 3

make sure you set the texture wrap parameters to GL_CLAMP_TO_EDGE in both S and T directions. Without this, the texture is incomplete and will appear black.

Answer 4

make sure that you are calling (glTexImage2D) with right formats(constants)
make sure that you are freeing resources of image after glTexImage2D
that's how i'm do it on android:
int[] textures = new int[1];
GLES20.glGenTextures(1, textures, 0);
mTextureID = textures[0];
GLES20.glBindTexture(GLES20.GL_TEXTURE_2D, mTextureID);
GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_MIN_FILTER,
GLES20.GL_NEAREST);
GLES20.glTexParameterf(GLES20.GL_TEXTURE_2D,
GLES20.GL_TEXTURE_MAG_FILTER,
GLES20.GL_LINEAR);
GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_S,
GLES20.GL_REPEAT);
GLES20.glTexParameteri(GLES20.GL_TEXTURE_2D, GLES20.GL_TEXTURE_WRAP_T,
GLES20.GL_REPEAT);
InputStream is = mContext.getResources()
.openRawResource(R.drawable.ywemmo2);
Bitmap bitmap;
try {
bitmap = BitmapFactory.decodeStream(is);
} finally {
try {
is.close();
} catch(IOException e) {
// Ignore.
}
GLUtils.texImage2D(GLES20.GL_TEXTURE_2D, 0, bitmap, 0);
bitmap.recycle();

Answer 5

maybe you forgot to
glEnable(GL_TEXTURE_2D);
is such case, texture2D in the shader would return black, as the OP seems to suffer.