Hi there,

I am currently in the course of porting Chocolate Doom to use SDL2's hardware scaling capability to render its buffer content to screen. For some background, Doom renders into a 8-bit paletted 320x200 pixel framebuffer that we want to seamlessly stretch to fill the entire screen, e.g. windows or full screen. On this way, however, we don't want to lose the gritty and pixelated look of the original Doom due to linear scaling or similar mechanisms which make the game appear too smooth and soft. We achieve this by upscaling the original framebuffer by an integer scale, i.e. without any interpolation, and then feeding it into the texture to scale it back to screen.

So, currently this means we have to blit the 8-bit paletted 320x200 surface into an intermediate RGBA 320x200 surface which we then scale up to 1280x800 by a scaled blit into another intermediate surface. This last surface is then loaded into the texture which is then scaled back into the renderer (with linear interpolation) and finally rendered to screen.

This sums up to a lot of intermediate surfaces and conversions between these surfaces which has proven to be a real performance killer. What I'd like to have is a means to directly do a scaled blit from the 320x200 8-bit surface into the upscaled 1280x800 RGBA surface that I can immediately load into the texture.

For reference, the initial implementation and discussion is here

https://github.com/chocolate-doom/chocolate-doom/commit/caf7461a4075352fd77b45dff58533900bd96e03

the latest commit introducing the additional intermediate surface can be found here

https://github.com/chocolate-doom/chocolate-doom/commit/777148cae2032bc2a33754329e7ecb52017a21cc

Thank you and best regards,

Fabian