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?
Related
My computer doesn't support OpenCL on the GPU or OpenGL compute shaders so I was wondering if it would be a straight forward process to get data from a vertex or fragment shader?
My goal is to pass 2 textures to the shader and have the shader computer the locations where one texture exists in the other. Where there is a pixel match. I need to retrieve the locations of possible matches from the shader.
Is this plausible? If so, how would I go about it? I have the basic OpenGL knowledge, I have set up a program that draws polygons with colors. I really just need a way to get position values back from the shader.
You can render to memory instead of to screen, and then fetch data from it.
Create and bind a Framebuffer Object
Create a Renderbuffer Object and attach it to the Framebuffer Object
Render your scene. The result will end up in the bound Framebuffer Object instead of on the screen.
Use glReadPixels to pull data from the Framebuffer Object.
Be aware that glReadPixels, like most methods of fetching data from GPU memory back to main memory, is slow and likely unsuitable for real-time applications. But it's the best you can do if you don't have features intended for that, like Compute Shaders, or are willing to do it asynchronously with Pixel Buffer Objects.
You can read more about Framebuffers here.
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.
I'm implementing an algorithm about pencil rendering. First, I should render the model using Phong shading to determine the intensity. Then I should map the texture to the rendered result.
I'm going to do a multipass rendering with opengl and cg shaders. Someone told me that I should try 'render to texture'. But I don't know how to use this method to get the effects that I want. In my opinion, we should first use this method to render the mesh, then we can get a 2D texture about the whole scene. Now that we have draw content to the framebuffer, next we should render to the screen, right? But how to use the rendered texture and do some post-processing on it? Can anybody show me some code or links about it?
I made this tutorial, it might help you : http://www.opengl-tutorial.org/intermediate-tutorials/tutorial-14-render-to-texture/
However, using RTT is overkill for what you're trying to do, I think. If you need the fragment's intensity in the texture, well, you already have it in your shader, so there is no need to render it twice...
Maybe this could be useful ? http://www.ozone3d.net/demos_projects/toon-snow.php
render to a texture with Phong shading
Draw that texture to the screen again in a full screen textured quad, applying a shader that does your desired operation.
I'll assume you need clarification on RTT and using it.
Essentially, your screen is a framebuffer (very similar to a texture); it's a 2D image at the end of the day. The idea of RTT is to capture that 2D image. To do this, the best way is to use a framebuffer object (FBO) (Google "framebuffer object", and click on the first link). From here, you have a 2D picture of your scene (you should check it by saving to an image file that it actually is what you want).
Once you have the image, you'll set up a 2D view and draw that image back onto the screen with an 800x600 quadrilateral or what-have-you. When drawing, you use a fragment program (shader), which transforms the brightness of the image into a greyscale value. You can output this, or you can use it as an offset to another, "pencil" texture.
I am trying to write a program that writes video camera frames into a quad.
I saw tutorials explaining that with framebuffers can be faster, but still learning how to do it.
But then besides the framebuffer, I found that there is also renderbuffers.
The question is, if the purpose is only to write a texture into a quad that will fill up the screen, do I really need a renderbuffer?
I understand that renderbuffers are for depth testing, which I think is only for checking Z position of the pixel, therefore would be silly to have to create a render buffer for my scenario, correct?
A framebuffer object is a place to stick images so that you can render to them. Color buffers, depth buffers, etc all go into a framebuffer object.
A renderbuffer is like a texture, but with two important differences:
It is always 2D and has no mipmaps. So it's always exactly 1 image.
You cannot read from a renderbuffer. You can attach them to an FBO and render to them, but you can't sample from them with a texture access or something.
So you're talking about two mostly separate concepts. Renderbuffers do not have to be "for depth testing." That is a common use case for renderbuffers, because if you're rendering the colors to a texture, you usually don't care about the depth. You need a depth because you need depth testing for hidden-surface removal. But you don't need to sample from that depth. So instead of making a depth texture, you make a depth renderbuffer.
But renderbuffers can also use colors rather than depth formats. You just can't attach them as textures. You can still blit from/to them, and you can still read them back with glReadPixels. You just can't read from them in a shader.
Oddly enough, this does nothing to answer your question:
The question is, if the purpose is only to write a texture into a quad that will fill up the screen, do I really need a renderbuffer?
I don't see why you need a framebuffer or a renderbuffer of any kind. A texture is a texture; just draw a textured quad.
In a Qt based application I want to execute a fragment shader on two textures (both 1000x1000 pixels).
I draw a rectangle and the fragment shader works fine.
But, now I want to renderer the output into GL_AUX0 frame buffer to let the result read back and save to a file.
Unfortunately if the window size is less than 1000x1000 pixels the output is not correct. Just the window size area is rendered onto the frame buffer.
How can I execute the frame buffer for the whole texture?
The recommended way to do off-screen processing is to use Framebuffer Objects (FBO). These buffers act similar the render buffers you already know, but are not constrained by the window resolution or color depths. You can use the GPGPU Framebuffer Object Class to hide low-level OpenGL commands and use the FBO right away. If you prefer doing this on your own, have a look at the extension specification.