vo: remove "slack" frames from swapchain

Those are controlled by the `--swapchain-depth` option and is already
set to 3 by default. There is no need to add hardcoded hidden frame of
"slack". Users can adjust depth by changing the config.

Author: kasper93

video/out/d3d11/context.c

@@ -548,9 +548,8 @@ static bool d3d11_init(struct ra_ctx *ctx)
         .color_space = p->opts->color_space,
         .configured_csp = &p->swapchain_csp,
         .flip = p->opts->flip,
-        // Add one frame for the backbuffer and one frame of "slack" to reduce
-        // contention with the window manager when acquiring the backbuffer
-        .length = vo_swapchain_depth(ctx->vo) + 2,
+        // Add one frame for the backbuffer
+        .length = vo_swapchain_depth(ctx->vo) + 1,
         .usage = usage,
     };
     if (!mp_d3d11_create_swapchain(p->device, ctx->log, &scopts, &p->swapchain))

video/out/opengl/context_angle.c

@@ -291,9 +291,8 @@ static bool d3d11_swapchain_surface_create(struct ra_ctx *ctx)
         .width = p->sc_width,
         .height = p->sc_height,
         .flip = o->flip,
-        // Add one frame for the backbuffer and one frame of "slack" to reduce
-        // contention with the window manager when acquiring the backbuffer
-        .length = vo_swapchain_depth(ctx->vo) + 2,
+        // Add one frame for the backbuffer
+        .length = vo_swapchain_depth(ctx->vo) + 1,
         .usage = DXGI_USAGE_RENDER_TARGET_OUTPUT | DXGI_USAGE_SHADER_INPUT,
     };
     if (!mp_d3d11_create_swapchain(p->d3d11_device, vo->log, &swapchain_opts,

video/out/opengl/context_dxinterop.c

@@ -339,9 +339,8 @@ static void fill_presentparams(struct ra_ctx *ctx,
         .Windowed = TRUE,
         .BackBufferWidth = ctx->vo->dwidth ? ctx->vo->dwidth : 1,
         .BackBufferHeight = ctx->vo->dheight ? ctx->vo->dheight : 1,
-        // Add one frame for the backbuffer and one frame of "slack" to reduce
-        // contention with the window manager when acquiring the backbuffer
-        .BackBufferCount = vo_swapchain_depth(ctx->vo) + 2,
+        // Add one frame for the backbuffer
+        .BackBufferCount = vo_swapchain_depth(ctx->vo) + 1,
         .SwapEffect = IsWindows7OrGreater() ? D3DSWAPEFFECT_FLIPEX : D3DSWAPEFFECT_FLIP,
         // Automatically get the backbuffer format from the display format
         .BackBufferFormat = D3DFMT_UNKNOWN,