Render Large Texture To Smaller Renderbuffer - ios

Question

I have a render buffer that is 852x640 and a texture that is 1280x720. When I render the texture, it is getting cropped, not just stretched. I know the aspect ratio needs correcting, but how can I get it so that the full texture displays in the render buffer?
//-------------------------------------
glGenFramebuffers(1, &frameBufferHandle);
glBindFramebuffer(GL_FRAMEBUFFER, frameBufferHandle);
glGenRenderbuffers(1, &renderBufferHandle);
glBindRenderbuffer(GL_RENDERBUFFER, renderBufferHandle);
[oglContext renderbufferStorage:GL_RENDERBUFFER fromDrawable:(CAEAGLLayer *)self.layer];
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_WIDTH, &renderBufferWidth);
glGetRenderbufferParameteriv(GL_RENDERBUFFER, GL_RENDERBUFFER_HEIGHT, &renderBufferHeight);
glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, renderBufferHandle);
//-------------------------------------
static const GLfloat squareVertices[] = {
-1.0f, 1.0f,
1.0f, 1.0f,
-1.0f, -1.0f,
1.0f, -1.0f
};
static const GLfloat horizontalFlipTextureCoordinates[] = {
0.0f, 1.0f,
1.0f, 1.0f,
0.0f, 0.0f,
1.0f, 0.0f,
};
size_t frameWidth = CVPixelBufferGetWidth(pixelBuffer);
size_t frameHeight = CVPixelBufferGetHeight(pixelBuffer);
CVReturn err = CVOpenGLESTextureCacheCreateTextureFromImage(kCFAllocatorDefault,
videoTextureCache,
pixelBuffer,
NULL,
GL_TEXTURE_2D,
GL_RGBA,
frameWidth,
frameHeight,
GL_BGRA,
GL_UNSIGNED_BYTE,
0,
&texture);
if (!texture || err) {
NSLog(#"CVOpenGLESTextureCacheCreateTextureFromImage failed (error: %d)", err);
return;
}
glBindTexture(CVOpenGLESTextureGetTarget(texture), CVOpenGLESTextureGetName(texture));
glViewport(0, 0, renderBufferWidth, renderBufferHeight); // setting this to 1280x720 fixes the aspect ratio but still crops
glBindFramebuffer(GL_FRAMEBUFFER, frameBufferHandle);
glUseProgram(shaderPrograms[PASSTHROUGH]);
// Update attribute values.
glVertexAttribPointer(ATTRIB_VERTEX, 2, GL_FLOAT, 0, 0, squareVertices);
glEnableVertexAttribArray(ATTRIB_VERTEX);
glVertexAttribPointer(ATTRIB_TEXTUREPOSITON, 2, GL_FLOAT, 0, 0, horizontalFlipTextureCoordinates);
glEnableVertexAttribArray(ATTRIB_TEXTUREPOSITON);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
// Present
glBindRenderbuffer(GL_RENDERBUFFER, renderBufferHandle);
[oglContext presentRenderbuffer:GL_RENDERBUFFER];
EDIT
I'm still running into issues. I've included more source. Basically, I need the entire raw input texture to display in wide screen while also writing the raw texture to disk.
When rendering to a smaller texture, things are automatically scaled, is this not the case with a renderbuffer?
I guess I could make another passthrough to a smaller texture, but that would slow things down.

Answer 1

First of all, keep glViewport(0, 0, renderBufferWidth, renderBufferHeight); with 852x640.
The problem is in your squareVertices - looks like it keeps coordinates that represent texture size. You need to set it equal to renderbuffer size.
The idea is that texture is mapped on your squareVertices rect. So you can render texture of any size mapped to rect of any size - texture image will be scaled to fit the rect.
[Update: square vertices]
In your case it should be:
{
0.0f, (float)renderBufferWidth/frameHeight,
(float)renderBufferWidth/frameWidth, (float)renderBufferHeight/frameHeight,
0.0f, 0.0f,
(float)renderBufferWidth/frameWidth, 0.0f,
};
But this is not good solution in common. From theory, the rectangle size on screen is determined by vertices position and transformation matrix. Each vertice is multiplied with matrix before rendering on screen. Looks like you don't set OpenGL projection matrix. With correct orthogonal projection your vertices should have pixel-equivalent positions.

Answer 2

Since I, Being new to OpenGL, remembers that the texture to be mapped should be in the powers of 2 by 2.
for eg the image resolution should be... 256x256, 512x512.
You can then SCALE the image using
gl.glScalef(x,y,z); function accordingly as per your requirements.
get the height and width accordingly and put these in your scalef function.
Try this, i hope this works.

Answer 3

Try these functions. My answer can be validated from the info #songhoa.ca.com
glGenFramebuffers()
void glGenFramebuffers(GLsizei n, GLuint* ids)
number of frame-buffers to create
void glDeleteFramebuffers(GLsizei n, const GLuint* ids)
pointer to a GLuint variable or an array to store a number of IDs.It returns the IDs of unused framebuffer objects. ID 0 means the default framebuffer, which is the window-system-provided framebuffer.
FBO may be deleted by calling glDeleteFramebuffers() when it is not used anymore.
glBindFramebuffer()
Once a FBO is created, it has to be bound before using it.
void glBindFramebuffer(GLenum target, GLuint id)
First parameter is The target should be GL_FRAMEBUFFER.
Second parameter is the ID of a framebuffer object.
Once a FBO is bound, all OpenGL operations affect onto the current bound framebuffer object. The object ID 0 is reserved for the default window-system provided framebuffer. Therefore, in order to unbind the current framebuffer (FBO), use ID 0 in glBindFramebuffer().
Try using those, or at least visit the link which could help you a lot. Sorry, i'm not experienced in OpenGL but I wanted to contribute the link, and explain the 2 functions. I think you can use the info to write your code.

Answer 4

Oh boy, so the answer is that this was working all along ;) It turns out the high resolution preset mode on the iPhone 4 actually covers less area than the medium resolution preset. This threw me in for a loop until Brigadir suggested what I should have done first all along, check the GPU snapshots.
I figured out the aspect ratio issue too by hacking the appropriate code in the GPUImage framework. https://github.com/bradLarson/GPUImage