OpenGL ES Framebuffer weird mirroring when drawing - iphone

Question

I really can't wrap my mind around this:
Previously I couldn't get Framebuffers to work, but I've got it going now. However, there is this incredibly weird mirroring going on with the texture generated from the framebuffer, and I have no idea why. Basically, I will try to draw a texture at 0,0 using GL_TRIANGLE_FAN, and the texture appears as normal (more or less) in the top right corner, but also appears in the bottom left corner, mirrored. If I fill up most or all of my viewport area with the same texture, the result is an ugly z-fighting overlap.
Screenshots will do this more justice.
Original image:
Original http://img301.imageshack.us/img301/1518/testsprite.png
Drawn 80x80 at (0,0)
80x80 http://img407.imageshack.us/img407/8339/screenshot20100106at315.png
Drawn 100x180 at (0,0)
100x180 http://img503.imageshack.us/img503/2584/screenshot20100106at316.png
Drawn 320x480 at (0,0)
320x480 http://img85.imageshack.us/img85/9172/screenshot20100106at317.png
And here is my code:
Set up the view:
//Apply the 2D orthographic perspective.
glViewport(0,0,320,480);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrthof(0, 320, 480, 0, -10000.0f, 100.0f);
//Disable depth testing.
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glDisable(GL_DEPTH_TEST);
//Enable vertext and texture coordinate arrays.
glEnableClientState(GL_VERTEX_ARRAY);
glEnableClientState(GL_TEXTURE_COORD_ARRAY);
glShadeModel(GL_SMOOTH);
glClearColor(0.5f, 0.5f, 0.5f, 1.0f);
glGetError(); // Clear error codes
sprite = [Sprite createSpriteFromImage:#"TestSprite.png"];
[sprite retain];
[self createTextureBuffer];
Create the texture buffer.
- (void) createTextureBuffer
{
// generate texture
glGenTextures(1, &bufferTexture);
glBindTexture(GL_TEXTURE_2D, bufferTexture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 512, 512, 0, GL_RGBA, GL_UNSIGNED_BYTE, NULL); // check if this is right
// generate FBO
glGenFramebuffersOES(1, &framebuffer);
glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);
// associate texture with FBO
glFramebufferTexture2DOES(GL_FRAMEBUFFER_OES, GL_COLOR_ATTACHMENT0_OES, GL_TEXTURE_2D, bufferTexture, 0);
// clear texture bind
glBindTexture(GL_TEXTURE_2D,0);
// check if it worked (probably worth doing :) )
GLuint status = glCheckFramebufferStatusOES(GL_FRAMEBUFFER_OES);
if (status != GL_FRAMEBUFFER_COMPLETE_OES)
{
printf("FBO didn't work...");
}
}
Run the render loop.
- (void)drawView
{
[self drawToTextureBuffer];
// Make sure that you are drawing to the current context
[EAGLContext setCurrentContext:context];
//Bind the GLView's buffer.
glBindFramebufferOES(GL_FRAMEBUFFER_OES, viewFramebuffer);
glViewport(0, 0, 320, 480);
//Clear the graphics context.
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
//Push the matrix so we can keep it as it was previously.
glPushMatrix();
//Rotate to match landscape mode.
glRotatef(90.0, 0, 0, 1);
glTranslatef(0.0f, -320.0f, 0.0f);
//Store the coordinates/dimensions from the rectangle.
float x = 0.0f;
float y = 0.0f;
float w = 480.0f;
float h = 320.0f;
// Set up an array of values to use as the sprite vertices.
GLfloat vertices[] =
{
x, y,
x, y+h,
x+w, y+h,
x+w, y
};
// Set up an array of values for the texture coordinates.
GLfloat texcoords[] =
{
0, 0,
0, 1,
1, 1,
0, 1
};
//Render the vertices by pointing to the arrays.
glVertexPointer(2, GL_FLOAT, 0, vertices);
glTexCoordPointer(2, GL_FLOAT, 0, texcoords);
// Set the texture parameters to use a linear filter when minifying.
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
//Enable 2D textures.
glEnable(GL_TEXTURE_2D);
//Bind this texture.
glBindTexture(GL_TEXTURE_2D, bufferTexture);
//Finally draw the arrays.
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
//Restore the model view matrix to prevent contamination.
glPopMatrix();
GLenum err = glGetError();
if (err != GL_NO_ERROR)
{
NSLog(#"Error on draw. glError: 0x%04X", err);
}
glBindRenderbufferOES(GL_RENDERBUFFER_OES, viewRenderbuffer);
[context presentRenderbuffer:GL_RENDERBUFFER_OES];
}
On the first pass, the render loop will draw the image into the FBO.
- (void)drawToTextureBuffer
{
if (!bufferWasCreated)
{
// render to FBO
glBindFramebufferOES(GL_FRAMEBUFFER_OES, framebuffer);
// set the viewport as the FBO isn't be the same dimension as the screen
glViewport(0, 0, 512, 512);
glPushMatrix();
//Store the coordinates/dimensions from the rectangle.
float x = 0.0f;
float y = 0.0f;
float w = 320.0f;
float h = 480.0f;
// Set up an array of values to use as the sprite vertices.
GLfloat vertices[] =
{
x, y,
x, y+h,
x+w, y+h,
x+w, y
};
// Set up an array of values for the texture coordinates.
GLfloat texcoords[] =
{
0, 0,
0, 1,
1, 1,
1, 0
};
//Render the vertices by pointing to the arrays.
glVertexPointer(2, GL_FLOAT, 0, vertices);
glTexCoordPointer(2, GL_FLOAT, 0, texcoords);
// Set the texture parameters to use a linear filter when minifying.
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
//Allow transparency and blending.
glEnable(GL_BLEND);
glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
//Enable 2D textures.
glEnable(GL_TEXTURE_2D);
//Bind this texture.
glBindTexture(GL_TEXTURE_2D, sprite.texture);
//Finally draw the arrays.
glDrawArrays(GL_TRIANGLE_FAN, 0, 4);
//Restore the model view matrix to prevent contamination.
glPopMatrix();
GLenum err = glGetError();
if (err != GL_NO_ERROR)
{
NSLog(#"Error on draw. glError: 0x%04X", err);
}
//Unbind this buffer.
glBindFramebufferOES(GL_FRAMEBUFFER_OES, 0);
bufferWasCreated = YES;
}
}

Answer 1

Your texcoords in - (void)drawView seem to be wrong
GLfloat texcoords[] =
{
0, 0,
0, 1,
1, 1,
0, 1 << HERE should be 1, 0
};