Render To Texture

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(Please see the .h file for complete documentation)

Dynamic Texture Class
This class will allow you to render to a texture and use it as...well whatever you want. The textures created are tracked by the texture manager and, though you'll need to re-capture, are otherwise not effected by resolution-changes etc. Please note that GL captures data starting from the bottom left, this means you will need to set up your texture coordinates with the y stuff flipped, or if you are using dglDrawBitmap make sure you specify a Y-flip

Render-to-texture emulation
OpenGL supports off-screen rendering buffers but only through platform-specific means and so I chose to do off-screen rendering simulation support by letting you store temporary pixels. This is all automated with the gui-rendering, for rendering other objects you will need to perform things in the following order:

dynamicTextureObject->setUpdateRect( updateRect );
dynamicTextureObject->storePixels();
//<your rendering code here, make sure you only draw in updateRect>
dynamicTextureObject->update();
dynamicTextureObject->restorePixels();

If you chose to use the off-screen rendering emulation please note that it is not a cheap operation, and I STRONGLY recomend that you
a) Enable the setUpdateRect optimization (see the description)
b) Use it as infrequently as possible

You are better off to do things before the canvas renders the content control in GuiCanvas::renderFrame, since the buffers will already have been swapped, and the user will be viewing the front buffer, then you can mess up the back-buffer all you want, grab your textures, then let the canvas render over it all. If you do this, just be wary of what you are putting into the depth/alpha buffers. Whatever you do, do NOT call glClear more than once per frame.

Example Screenshot
The screenshot is from my game-in-progress, Gridwalkers, which is what I coded this object for. It was done by rendering the root-GUI object to a texture and then using dglDrawBitmapStretch to draw it after all the controls were rendered. As you can see, the console covers up the 'Quit' button and the GG logo, however they are still visible on the texture. The texture is updated every frame as well. In order to do this, I had to reset the update rects every frame, otherwise the canvas will only draw the dirty areas, which usually is just the area under the mouse cursor, unless a control signs up to have it's rect redrawn.

The higher resolution version of the screenshot can be found here

This is not 100% bullet-proof or heavily tested. Treat it as such. If you have any problems with this, post to the forums. I suggest putting the code in 'dgl' since that is where it seems to fit best, your milage may vary.


For more examples of what you can do with Render-To-Texture, a feedback loop, and a little pixel-shader magic:
Screen Wipe 1
Screen Wipe 2
Screen Wipe 3
(No I'm not releasing that code)