Question About OpenGL Performance using Memory DC

OpenGL
1

I am a beginner. I am not sure whether this is the right place to ask the following question. thank you.

An OpenGL Application renders snowworld, whose size is 1024 x 768.

Method 1. Create OpenGL render context using window DC.
The load of CPU is below 1%.

Method 2. Create OpenGL render context using memory DC.
Copy the content in memory DC to the window DC using bitblt.
The load of CPU is below 100%.

Why the load in method 2 is so heavy? how to optimize the performance using memory DC?

Thank you very much!

2

Memory DC is not accelerated by your graphics card. If you want offscreen rendering, use the framebuffer object extension.

3

Thank Zengar very much!

Where can I find the document about framebuffer object extension.

4

simple sample on how to use them:
http://www.codesampler.com/oglsrc/oglsrc_14.htm#ogl_frame_buffer_object

spec:
http://oss.sgi.com/projects/ogl-sample/registry/EXT/framebuffer_object.txt

5

http://www.opengl.org/wiki/index.php/GL_EXT_framebuffer_object

6

Other samples:
http://www.g-truc.net/sample-ogl2.html#sample11
http://www.g-truc.net/sample-ogl2.html#sample10
http://www.g-truc.net/sample-ogl2.html#sample09
http://www.g-truc.net/sample-ogl2.html#sample08
http://www.g-truc.net/sample-ogl2.html#sample07
http://www.g-truc.net/sample-ogl2.html#sample06

7

And for the adventurous OpenGL 3.0 enthusiast, FBO is now in the core spec

http://www.opengl.org/registry/doc/glspec30.20080923.pdf

Currently requires an NVIDIA GeForce 8xxx or better with the drivers to be found over here

http://developer.nvidia.com/object/opengl_3_driver.html

More info in the thread over here

http://www.opengl.org/discussion_boards/ubbthreads.php?ubb=showflat&Number=243747#Post243747

8

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