Possible unnecessary screen clearing

[xoltra]

I've noticed that darkplaces clears the screen each frame which may not be necessary. Normally the color buffer only needs to be cleared if there is some chance that the entire screen will not be written to. Since most correct non-leaky maps should always paint the entire screen not clearing the color buffer each frame should not be a problem.

I've tried removing the GL_COLOR_BUFFER_BIT flag from all calls to GL_Clear() and qglClear() other than the one time call in GL_Init(). The rendering is not noticeably changed other than the fact that leaks in leaky maps are no longer black, but just not painted. Also the Alien Trap logo was not removed perfectly.

[LordHavoc]

I've noticed that darkplaces clears the screen each frame which may not be necessary. Normally the color buffer only needs to be cleared if there is some chance that the entire screen will not be written to. Since most correct non-leaky maps should always paint the entire screen not clearing the color buffer each frame should not be a problem.

I've tried removing the GL_COLOR_BUFFER_BIT flag from all calls to GL_Clear() and qglClear() other than the one time call in GL_Init(). The rendering is not noticeably changed other than the fact that leaks in leaky maps are no longer black, but just not painted. Also the Alien Trap logo was not removed perfectly.

In my testing I've found no noteworthy slowdown from clearing the color buffer (something like 0.1% loss).

And your testing was not thorough enough - try reducing the viewsize below 100 and then watching notify lines stack up on the uncleared areas of the screen around the view..

This is also an issue if there is no view (such as when disconnected).

[xoltra]

I'm glad that you've thought about it and tested it more thoroughly than I have. I only brought it up because another game I'm familiar with (Sauerbraten) avoids clearing the color buffer each frame, but if in your testing the impact is that small then there is no need to worry about it.

[kyre]

Actually, due to color buffer (bandwidth) compression on newer graphics cards clearing the screen every frame can be faster than not clearing it at all.

Same with Z-buffer clears, chips with hierarchal z buffers/fast clears usually run slower with the old quake z-trick (which avoids clearing the buffer by chopping the buffer in half and alternating the comparison direction each frame), than just clearing each frame.

It all boils down to which alternative happen to use the least amount of memory accesses on a particular chip.

[Tei]

On Telejano I just disable to ability to change clear, and force clear always. This able to make maps withouth sky or with a invisible sky. I even tint the color clearing to the fog color, so the infinite as the color of fog.