d3d11/swapchain: add pl_d3d11_swapchain_params.{alpha,color}_bits

Author: kasper93

meson.build

@@ -12,6 +12,7 @@ project('libplacebo', ['c', 'cpp'],
     7,
     # API version
     {
+      '360': 'add pl_d3d11_swapchain_params.{alpha,color}_bits',
       '359': 'add pl_vulkan_swapchain_params.{alpha,color}_bits',
       '358': 'add PL_COLOR_SYSTEM_YCGCO_{RE,RO}',
       '357': 'add pl_daylight_from_temp, pl_blackbody_from_temp, and generalize pl_white_from_temp',

src/d3d11/swapchain.c

@@ -338,15 +338,26 @@ static enum DXGI_FORMAT pick_format(pl_swapchain sw,
     struct priv *p = PL_PRIV(sw);
     struct d3d11_ctx *ctx = p->ctx;
 
+    // Allow 16-bit, which is scRGB in practice, only if explicitly requested.
+    // Shouldn't be used as it's not fully supported in libplacebo yet.
+    bool use_16_bits = p->params.alpha_bits > 8 || p->params.color_bits > 10;
+
+    // TODO: add proper support for scRGB (DXGI_FORMAT_R16G16B16A16_FLOAT)
+    if (use_16_bits && d3d11_format_supported(ctx, DXGI_FORMAT_R16G16B16A16_FLOAT))
+        return DXGI_FORMAT_R16G16B16A16_FLOAT;
+
     bool use_10_bits = pl_color_space_is_hdr(hint) ||
                        pl_color_primaries_is_wide_gamut(hint->primaries) ||
                        !p->params.disable_10bit_sdr;
+    // If >2 alpha bits are requested, don't use rgb10a2, drop to rgba8 instead.
+    // This will most likely disable HDR output as well, but without scRGB support
+    // there's no better alternative.
+    if (p->params.alpha_bits > 2)
+        use_10_bits = false;
 
     if (use_10_bits && d3d11_format_supported(ctx, DXGI_FORMAT_R10G10B10A2_UNORM))
         return DXGI_FORMAT_R10G10B10A2_UNORM;
 
-    // TODO: add support for scRGB (DXGI_FORMAT_R16G16B16A16_FLOAT)
-
     return DXGI_FORMAT_R8G8B8A8_UNORM;
 }
 

src/include/libplacebo/d3d11.h

@@ -197,6 +197,18 @@ struct pl_d3d11_swapchain_params {
 
     // Disable using a 10-bit swapchain format for SDR output
     bool disable_10bit_sdr;
+
+    // Minimum number of alpha bits requested in the swapchain format. In
+    // practice, this can be used to prefer formats with higher alpha bit depth
+    // (e.g. rgba8/rgba16 over rgb10a2), potentially trading 2 bits per color
+    // channel for increased alpha precision. This is a hint, if no matching
+    // format is found, lower bit depths will be accepted.
+    uint8_t alpha_bits;
+
+    // Minimum number of color bits requested in the swapchain format. This can
+    // be used to prefer formats with higher color bit depth. This is a hint,
+    // if no matching format is found, lower bit depths will be accepted.
+    uint8_t color_bits;
 };
 
 #define pl_d3d11_swapchain_params(...) (&(struct pl_d3d11_swapchain_params) { __VA_ARGS__ })