Image Rotation with 1 degree precision using OpenGL

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i want to rotate an BMP image with 1 degree precision by using OpenGL and i want to Export the Rotated image & save is as BMP file.

Could anyone please tell me is it possible by using standard functions in OpenGL?
Thanks

Posted 18-Jun-13 1:33am

Balaji_mcr

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nv3 18-Jun-13 9:26am

Did you mean OpenCV instead of OpenGL? If yes, see warpAffine.

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JackDingler · Accepted Answer · 2013-06-18T03:24:00

Solution 1

Most of it can be done in OpenGL.

Loading and saving images isn't an OpenGL function though.

To do this you need to load the bitmap into memory.
Create a destination bitmap in memory.
Set Open GL to render to your destination bitmap.
Apply the original bitmap as a texture to a square mesh.
Rotate the mesh.
Render the mesh.
Save the destination bitmap.

This link describes how to render to a texture.
http://www.opengl-tutorial.org/intermediate-tutorials/tutorial-14-render-to-texture/[^]

Note that some OpenGL functions use the GL_RGB parameter.
For 24 bit windows bitmaps, you can use GL_BGR instead, as windows has the Red Green and Blue reversed.
For 32 bit windows bitmaps, use GL_BGRA

These settings allow you to use the bitmap buffers directly, without the need for code that corrects the color order.

Posted 18-Jun-13 3:24am

JackDingler

Updated 19-Jun-13 7:21am

v5

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Balaji_mcr 19-Jun-13 2:11am

Thank you for your reply @jack
I've tried rendering an Image by making it as a texture to a Quad & i am also able to rotate this image(Quad). But i want to save this rotated image. is it possible? can u refer any link regarding this process?

JackDingler 19-Jun-13 13:20pm

I updated the solution for you.

Balaji_mcr 20-Jun-13 1:33am

Thank you for your update@jack
i've used glReadPixels() to read this rotated image as a buffer & i exported it. But it takes too much time....

JackDingler 20-Jun-13 11:58am

I did a bit of googling on glReadPixels() and that seems to be the way to go.

I also saw that GL_BGR(A) tends to be faster on windows machines than GL_(A)RGB...

When you call glReadPixels() you're asking the CPU to copy memory from the graphics card to your machine's RAM. This will take time.

A suggestion I saw a number of times for applications needing a high framerate is to double buffer so that you're rendering on one FBO and copying to the CPU from another. With each operation you swap FBOs.

If you need even faster performance, perhaps using NVidia Hardware and CUDA could be your solution. In CUDA, your CPU and Graphics card share memory, so there's no need to copy across the bus, to another memory region on read.

Balaji_mcr 21-Jun-13 1:53am

Thank you for your suggestion @jack.
I'm working on it...