Rendering A Texture Onto Itself In OpenGL ES

Question

I can comfortably render a scene to a texture and map that texture back onto a framebuffer for screen display. But what if I wanted to map the texture back onto itself in order to blur it (say, at a quarter opacity in a new location). Is that possible?

The way I've done it is simply to enable the texture:

glEnable(GL_TEXTURE_2D);
glBindTexture(GL_TEXTURE_2D, color_tex);

And then draw to it:

glVertexPointer(2, GL_FLOAT, 0, sv);
glTexCoordPointer(2, GL_FLOAT, 0, tcb1);
glColor4f (1.0f,1.0f,1.0f,0.25f);
glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);

(some code omitted, obviously)

Is there anything obviously wrong with that idea? Am I being an idiot?

Answer 1

No, you can't write the texture to the same texture, that triggers undefined behaviour.

But you can use a technique called Ping-Pong rendering, so you draw the result of the operation into another texture, and if you need to do more processing, you write the result to the first texture.