Renderer texture clipping no longer respects scale (SDL_SetRenderScale)

[AntTheAlchemist]

A recent change has caused textures to be cut-off from being drawn (clipped) when a scale is being set. Seems to affecting all renderers and platforms.

SDL_SetRenderScale(renderer, 0.5f, 0.5f) will see textures only being draw on the top-left quarter of the window.

The cause of this will probably be clear to whomever made a recent commit relating to texture clipping logic / viewport.

[slouken]

@icculus probably knows what's going on here.

[AntTheAlchemist]

A little test to reproduce. SDL_RenderDebugText is SO useful!

#include <SDL3/SDL_main.h>
#include <SDL3/SDL.h>
int main(int argc, char** argv) {
	SDL_Init(SDL_INIT_VIDEO);
	SDL_Window* win = SDL_CreateWindow(nullptr, 500, 500, SDL_WINDOW_RESIZABLE | SDL_WINDOW_HIGH_PIXEL_DENSITY);
	SDL_Renderer* ren = SDL_CreateRenderer(win, nullptr);
	SDL_SetRenderVSync(ren, 1);
	SDL_SetRenderScale(ren, 0.5f, 0.5f);
	bool running = true;
	while(running) {
		SDL_PumpEvents();
		SDL_Event event;
		while (SDL_PeepEvents(&event, 1, SDL_GETEVENT, SDL_EVENT_FIRST, SDL_EVENT_LAST) == 1) {
			switch (event.type) {
			case SDL_EVENT_QUIT:
				running = false;
				break;
			}
		}
		SDL_SetRenderDrawColor(ren, 0, 0, 0, SDL_ALPHA_OPAQUE);
		SDL_RenderClear(ren);
		SDL_SetRenderDrawColor(ren, 0, 255, 0, SDL_ALPHA_OPAQUE);
		for(int r = 0; r < 500; r++) 
			SDL_RenderDebugText(ren, SDL_randf() * 1000, SDL_randf() * 1000, "*");
		SDL_RenderPresent(ren);
		SDL_Delay(100);
	}
	SDL_DestroyRenderer(ren);
	SDL_DestroyWindow(win);
	SDL_Quit();
	return 0;
}

[AntTheAlchemist]

Ah, yes. ef758d0 broke things for me.

[icculus]

Okay, so what's happening here is two things:

• SDL_SetRenderScale is (currently) affecting a bunch of stuff it shouldn't: cliprect, viewport, event coordinate conversion. But it should probably only be used by primitive drawing functions like SDL_RenderLines and SDL_RenderTexture, etc. The thing that should affect all that stuff globally is logical presentation and not scale (although both apply and are multiplied together for a final scale when drawing primitives). SDL_RenderSetScale should be more like one-off calls to bump a single texture draw larger and then it gets set to something else for the next draw call. The current documentation is vague about this in some places and outright conflicting in others and should be corrected (unless I'm totally wrong about the intention here).
• SDL_RenderTexture doesn't take the scale into account when deciding to dump a draw that's totally off-screen. I can fix that, but I'd argue that all the lower level systems (either the backends, the GPU drivers, or the GPU itself) need to have these checks anyhow, so let's let them drop things after scale is applied, and remove the check from SDL_RenderTexture completely, instead of adding more math.

I've got patches to change this, but before I push them, I just want to make sure we all agree that reducing the scope of SDL_SetRenderScale's influence is the correct and least-surprising thing to do.

[slouken]

• SDL_SetRenderScale is (currently) affecting a bunch of stuff it shouldn't: cliprect, viewport, event coordinate conversion. But it should probably only be used by primitive drawing functions like SDL_RenderLines and SDL_RenderTexture, etc. The thing that should affect all that stuff globally is logical presentation and not scale (although both apply and are multiplied together for a final scale when drawing primitives). SDL_RenderSetScale should be more like one-off calls to bump a single texture draw larger and then it gets set to something else for the next draw call. The current documentation is vague about this in some places and outright conflicting in others and should be corrected (unless I'm totally wrong about the intention here).

In SDL2 it affects everything because it was used to implement logical presentation, which virtualizes all your drawing. I think that's still the intention in case applications want to use it that way for their own custom logical presentation (and makes it possible for sdl2-compat to do the right thing).

• SDL_RenderTexture doesn't take the scale into account when deciding to dump a draw that's totally off-screen. I can fix that, but I'd argue that all the lower level systems (either the backends, the GPU drivers, or the GPU itself) need to have these checks anyhow, so let's let them drop things after scale is applied, and remove the check from SDL_RenderTexture completely, instead of adding more math.

That seems reasonable. The GPU should cull everything that's completely outside the viewport and I know we early out in the software blit code in that case.

[icculus]

I'm not sure I agree about SDL_RenderSetScale, but we'll leave it as-is. The other fix is in now and makes this test program work as intended.