Noticeable screen tearing in SDL 3.4.0 compared to SDL 3.2.22 (without vsync)

[yughias]

Description

After upgrading from SDL 3.2.2 to SDL 3.4.0, I’m observing significantly more visible screen tearing while using the same project and rendering code.

The tearing is especially noticeable in my main loop, which appeared stable when using SDL 3.2.2.

Additional context

• VSync is disabled.
• The main loop runs at a floating-point (non-integer) refresh rate.
• Rendering is done via SDL_Renderer and a streaming texture.

I understand that tearing can occur without vsync by design. However, the behavior is noticeably more pronounced in SDL 3.4.0 compared to earlier versions.

This raises the question of whether relevant changes were introduced between these versions, for example:

• A change in rendering behavior, or presentation defaults between SDL 3.2.2 and SDL 3.4.0, or
• The previous version implicitly masking or reducing tearing under similar conditions.

Main loop

while (running) {
    Uint64 targetFrameTime = (Uint64)(1e9 / frameRate);
    a_clock = SDL_GetTicksNS();
    Uint64 deltaNS = a_clock - b_clock;

    if (deltaNS >= targetFrameTime) {
        deltaTime = deltaNS / 1e6f;

        mainloop();
        renderBufferToWindow();

        b_clock = a_clock;
    } else {
        Uint64 remaining = targetFrameTime - deltaNS;
        if (remaining > 1e6)
            SDL_DelayPrecise(remaining - 1e6);
    }
}

void renderBufferToWindow() {
    SDL_Surface* locked_surface;
    SDL_LockTextureToSurface(drawBuffer, NULL, &locked_surface);
    SDL_BlitSurface(front_surface, NULL, locked_surface, NULL);
    SDL_UnlockTexture(drawBuffer);

    SDL_RenderClear(renderer);
    SDL_RenderTexture(renderer, drawBuffer, NULL, NULL);
    SDL_RenderPresent(renderer);
}

Expected behavior

Either:

• Tearing behavior comparable to SDL 3.2.2 under the same conditions, or
• Confirmation that the increased tearing in SDL 3.4.0 is expected and intentional.

[LemonFountainPerson]

I've also experienced this issue. Ever since updating to 3.4.0, with no changes to my code I've been experiencing significant screen tearing where I was previously seeing none. My project has multiple instances of loaded (not streamed) textures, and in addition this seems to happen even when there is only one such texture being rendered to the screen. I'm wondering if this is intentional behaviour or if this is a bug?

[icculus]

Vsync defaults got changed to off around this time for some platforms. If tearing has increased dramatically, it's likely you thought vsync was 0 but it wasn't.

[yughias]

I can confirm vsync was off also in previous version, since my program had deltatimes between one frame and the next one that were not equal to the screen refresh rate.

[LemonFountainPerson]

I can also confirm that while using the older SDL version I was getting 3000+ fps on my project, with no visible screen tearing. I even tested this again today by swapping out the SDL dlls for older versions and I was able to recreate this behaviour.

[slouken]

Can you git bisect to find out where this changed?

[icculus]

I'd be curious to know if there's a specific commit that's a culprit. We do literally nothing to prevent tearing beyond vsync, but maybe some apparently-unrelated thing had a side-effect?

Definitely bisect it. I'm not sure we can promise much here regardless of the results, though, if enabling vsync is out of the question, but knowing more about the situation would be very helpful!

[LemonFountainPerson]

I've done slightly more testing and discovered this isn't an issue on linux, and I was only experiencing screen tearing specifically with SDL 3.4.0 on Windows 11. It seems to work fine on linux regardless of vsync.

[slouken]

I've done slightly more testing and discovered this isn't an issue on linux, and I was only experiencing screen tearing specifically with SDL 3.4.0 on Windows 11. It seems to work fine on linux regardless of vsync.

If you can git bisect it to a specific commit, we can take a look right away, otherwise we'll bump this out of the shipping milestone.

[icculus]

I'm going to bump this for now, but if you get a chance to bisect, we would love to hear about it whenever you are able, regardless of the current milestone.

[Kontrabant]

I've done slightly more testing and discovered this isn't an issue on linux, and I was only experiencing screen tearing specifically with SDL 3.4.0 on Windows 11. It seems to work fine on linux regardless of vsync.

A bit of additional info here: I'm not sure what renderer you are using, but OpenGL on Linux/Wayland generally defaults to mailbox mode when running unthrottled, so there will be no tearing by default. Some compositors do allow tearing, and, if supported, it can usually be enabled in the display settings (KDE/Wayland has a "Screen Tearing" checkbox in the display settings).