I need an OpenGL buffer to draw on and retrieve pixel values from. I would also like to draw this buffer onto the display buffer.
I'd like an example of how I can do this.
Frame Buffer Objects (FBOs) would work.
Related
I want to display a 2D array of pixels directly to the screen. The pixel-data is not static and changes on user triggered event like a mousemove. I wish to have a display framebuffer to which I could write directly to the screen.
I have tried to create a texture with glTexImage2D(). I then render this texture to a QUAD. And then I update the texture with glTexSubImage2D() whenever a pixel is modified.
It works!
But this is not the efficient way I guess. The glTexSubImage2D copies whole array including the unmodified pixels back to the texture which is not good performance wise.
Is there any other way, like having a "display-framebuffer" to which I could write only the modified pixels and change will reflect on the screen.
glBlitFramebuffer is what you want.
Copies a rectangular block of pixels from one frame buffer to another. Can stretch or compress, but doesn't go through shaders and whatnot.
You'll probably also need some combination of glBindFramebuffer, glFramebufferTexture, glReadBuffer to set up the source and destination.
In my computer shader I am filling my SBBO with ARGB value's. (I could easily change this to RGBA though). But now I'd like to draw the buffer I filled to the screen.
What is the best way to do this, and could you mayby provide an example?
Is there any way to attach a texture buffer object (ARB_texture_buffer_object) to a framebuffer (EXT_framebuffer_object), so that I can directly render into the texture buffer object?
I need this to make an exact, bit-wise copy of a multisample framebuffer (color buffer, depth buffer and stencil buffer), and have this copy reside in main memory rather than VRAM.
UPDATE:
The problem is that I cannot directly call glReadPixels on a multi sampled frame buffer, to copy its contents. Instead, I have to blit the multi sampled frame buffer to an intermediate frame buffer and then call glReadPixels on that. During this process, multiple samples are averaged and written to the intermediate buffer. There is now, of course, a loss in precision if I restore this buffer with glWritePixels.
I realize that I can use a multi sample texture as the backing storage for a frame buffer object, but this texture will reside in VRAM and there appears to be no way of copying it to main memory without the same loss of precision. Specifically, I am worried about a loss of precision pertinent to the multi sampled depth buffer attachment, rather than the color buffer.
Is there another way to make an exact copy (and restore this copy) of a multi sampled frame buffer in OpenGL?
TL;DR: How to copy the exact contents of a multi sample frame buffer (specifically, depth buffer) to main memory and restore those contents later, without a loss of precision.
OpenGL does not allow you to bind a buffer texture as a render target. However, I don't see what is stopping you from making "an exact, bit-wise copy of a multisample framebuffer". What problem are you encountering that you believe buffer textures can solve?
How to copy the exact contents of a multi sample frame buffer (specifically, depth buffer) to main memory and restore those contents later, without a loss of precision.
No.
And you don't need to copy the contents of an image to main memory to be able to save and restore it later. If you need to preserve the contents of a multisample image, simply blit it to another multisample image. You can blit it back to restore it. Or better yet, render to a multisample texture that you don't erase until you're done with it. That way, there's no need for any copying.
This is a question about syncronization in OpenGL. And the question is:
At which point in the following (pseudo) code sample does syncronization happen.
// 1.
try to map buffer object (write only and invalidate buffer)
copy new data to mapped buffer
unmap buffer
// 2.
bind buffer
call subteximage to fill texture from buffer
unbind buffer
// 3.
render with texture
As far as i know syncronization happens as soon as 'an object is used'. Now it's questionable if the texture is used if it is filled from the buffer or if it is used in rendering.
If glSubTexImage doesn't block it would be possible to generally stream texture data by using buffer updates in texture update calls.
Florian
Your code can block anywhere between copy and glFlush after render with texture (or frame buffer swap). It's up to the implementation.
What is the difference between FBO and PBO? Which one should I use for off-screen rendering?
What is the difference between FBO and PBO?
A better question is how are they similar. The only thing that is similar about them is their names.
A Framebuffer Object (note the capitalization: framebuffer is one word, not two) is an object that contains multiple images which can be used as render targets.
A Pixel Buffer Object is:
A Buffer Object. FBOs are not buffer objects. Again: framebuffer is one word.
A buffer object that is used for asynchronous uploading/downloading of pixel data to/from images.
If you want to render to a texture or just a non-screen framebuffer, then you use FBOs. If you're trying to read pixel data back to your application asynchronously, or you're trying to transfer pixel data to OpenGL images asynchronously, then you use PBOs.
They're nothing alike.
A FBO (Framebuffer object) is a target where you can render images other than the default frame buffer or screen.
A PBO (Pixel Buffer Object) allows asynchronous transfers of pixel data to and from the device. This can be helpful to improve overall performance when rendering if you have other things that can be done while waiting for the pixel transfer.
I would read VBOs, PBOs and FBOs:
Apple has posted two very nice bits of
sample code demonstrating PBOs and
FBOs. Even though these are
Mac-specific, as sample code they're
good on any platoform because PBOs and
FBOs are OpenGL extensions, not
windowing system extensions.
So what are all these objects? Here's
the situation:
I want to highlight something.
FBO it not memory block. I think it look like struct of pointer. You Must attach Texture to FBO to use it. After attach Texture you now can draw to it for offscreen render or for second pass effect.
struct FBO{
AttachColor0 *ptr0;
AttachColor1 *ptr1;
AttachColor2 *ptr2;
AttachDepth *ptr3;
};
In the other hand, PBO is memory block "block to hold type of memory. "Try to think of it as malloc of x size, then you can use memcpy to copy data from it to texture/FBO or to it".
Why to use PBO?
Create intermediate memory buffer to interface with Host memory and not stop OpenGL drawing will upload texture to or from host.