I want to enable rendering in specified points (I am holding the collection of points in array) and disable rendering on rest of OpenGL layer
can any one help me to get out of this problem for iPhone!!!!
If you're using OpenGL ES 2.0, you can use the stencil buffer to mask those areas.
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I want to implement image edition using OpenGL shaders. I have found some examples how to implement off-screen rendering using OpenGL ES1.
Do you now any example about off-screen rendering using OpenGL ES2 ans shaders on iPhone?
Thank you in advance
You need to use the framebuffer object extension (FBO), which is part of OpenGL ES2.
This is the same way as with OpenGL ES 1.0, except the functions lose their OES suffix (because FBO was an OES extension to ES1, not a part of the core).
You might like http://programming4.us/multimedia/3288.aspx this tutorial. The code is pretty simple and should be pretty easy to use it with GLES2.
I need help setting up multi-pass rendering with OpenGL ES 2.0 on the iPhone. I haven't been able to find an example which implements both rendering to a texture and multi-pass shading.
I'm looking for some instructions and sample code which implement:
First stage: Render to a texture
Second stage: Input that texture and render to screen
I have referenced Apple's OpenGL ES Programming Guide, OpenGL Shading Language (Orange Book), and O'Reilly's iPhone 3D Programming Book.
The Orange Book discusses deferred shading and provides two shader programs for first-pass and second-pass rendering, but doesn't provide example code to setup that application or show how to communicate data between both shaders.
Questions:
How to render to texture?
Using glDrawElements
How to input that texture to the next pass?
How to implement two shading programs?
How to alternate first- and second-pass shading programs?
Need to attach, detach, and call 'use' for each pass?
How to implement multi-pass shading?
I wrote a short example of doing just this (multiple render-to-texture passes on the iPhone using OpenGL ES 2.0) a few weeks ago: http://www.mat.ucsb.edu/a.forbes/blog/?p=245
**
Edit, this post is a bit old, and it has moved here:
http://blog.angusforbes.com/openglglsl-render-to-texture/
**
Ok, first of all: I'm no expert on OpenGL ES 2.0. I was kind of in the same situation where I wanted to do a multipass render setup, in one of my first OpenGL ES applications.
I also used the Orange Book. Check chapter 12. Framebuffer Objects > Examples. The first example demonstrates how to use a framebuffer to render to a texture, and then draws that texture to screen.
Basically using that example I created an application that renders some geometry to a texture using an effect shader, then renders that texture to screen, layered with some other content all using a different shader.
I'm not sure if this is the best approach, but it works for my purposes. My setup:
I create two framebuffers, the default and an offscreen one. Same for the renderbuffers
I create a texture which the app will render to
I bind the offscreen framebuffer, and attach the texture to it using glFramebufferTexture2D
My rendering:
bind the offscreen framebuffer.
use my first shader program
draw my geometry
bind the default framebuffer
use my second shader program
draw a fullscreen quad with the texture attached to it.
I'm doing heavy computation using the GPU, which involves a lot of render-to-texture operations. It's an iterative computation, so there's a lot of rendering to a texture, then rendering that texture to another texture, then rendering the second texture back to the first texture and so on, passing the texture through a shader each time.
My question is: is it better to have a separate FBO for each texture I want to render into, or should I rather have one FBO and bind the target texture using glFramebufferTexture2D each time I want to change render target?
My platform is OpenGL ES 2.0 on the iPhone.
On the iPhone implementation, it is inexpensive to change the attachment, assuming the old and new textures are the same dimensions/format/etc. Otherwise, the driver has to do some additional work to reconfigure the framebuffer.
AFAIK, better performance is achieved by using only one FBO, and changing the texture attachments as necessary.
The best way is to do benchmark.
How big of a difference is the description language of Quartz2d to OpenGL ES?
It seems they are similar in description power... except that Quartz is mostly 2d and that OpenGL is out of the box 3d ( but can be made 2d focused ).
Are the mappings from 2dQuartz to 2d OpenGL ES that different? Im sure there must be differences in some specific features that might be handled differently on one vs another... but to do a translator?
Anyone have experience with both OpenGL and Quartz2d have some insights?
Quartz and OpenGL ES are two completely different animals. While they both have a C-based API that deals with a state machine and that draws into a context, their purposes are dissimilar. In Quartz you specify lines, Bezier and quadratic curves, arcs, or rectangles, as well as fills, gradients, and shadows / glows. In OpenGL ES, you provide vertices, raster textures, and lighting information, from which a scene is generated.
They are both useful in particular cases. You might draw a 2-D static element using Quartz, into a view, layer, or texture, and then place and move that view or layer in 3-D space using Core Animation or do the same for a texture using OpenGL ES.
Rather than try to overlay one API on the other, use whichever is more appropriate for what you are doing, or look to a framework like cocos2d which lets you build and animate 2-D scenes or Core Animation where you can do Quartz drawing into a layer but still use a nicely abstracted API for moving these layers around.
I am trying to Google for what I've mentioned in the title, but somehow I couldn't find it. This should not be that hard, should it?
What I am looking for is a way to gain access to an OpenGL ES texture on iPhone, and a way to get/set pixel with it. What are the OpenGL ES functions I am looking for?
Before OpenGL ES is able to see your texture, you should have loaded it in memory already, generated texture names(glGenTextures), and bound it(glBindTexture). Your texture data is just a big array in memory.
Therefore, should you with to change a single texel, you can manipulate it in-memory and then bind it again. This approach is usually done for procedural texture generation. There are many available resources on the net about it, for instance: http://www.blumtnwerx.com/blog/2009/06/opengl-es-texture-mapping-for-iphone-oolong-powervr/
While glReadPixels is available, there are very few situations where you'd need to use it for interactive applications(screen capture comes to mind). It absolutely destroys performance. And still won't give you back the original textures, but instead will return a block of the framebuffer.
I have no idea what kind of effect you are looking for. However, if you are targeting a device that supports pixel shaders, perhaps a custom pixel shader can do what you want.
Of course, I am working under the assumption you didn't mean pixel as in screen coordinates.
I don't know about setting an individual pixel, but glReadPixels can read a block of pixels from the frame buffer (http://www.khronos.org/opengles/sdk/docs/man/glReadPixels.xml). Your problem googling may be because texture pixels are often shortened to 'texels'.