[d3d9] Implement d3d9.forceSwapchainMSAA

Works good enough for some titles like Vampire The Masquerade: Bloodlines.

dxvk.conf

@@ -289,3 +289,9 @@
 
 # d3d9.enableDialogMode = False
 
+# Overrides the application's MSAA level on the swapchain
+# 
+# Supported values: -1 (application) and 0 to 16 (user override)
+
+# d3d9.forceSwapchainMSAA  = -1
+

src/d3d9/d3d9_options.cpp

@@ -62,6 +62,7 @@ namespace dxvk {
     this->supportVCache         = config.getOption<bool>    ("d3d9.supportVCache",         vendorId == 0x10de);
     this->enableDialogMode      = config.getOption<bool>    ("d3d9.enableDialogMode",      false);
     this->forceSamplerTypeSpecConstants = config.getOption<bool> ("d3d9.forceSamplerTypeSpecConstants", false);
+    this->forceSwapchainMSAA    = config.getOption<int32_t> ("d3d9.forceSwapchainMSAA",    -1);
 
     this->forceAspectRatio      = config.getOption<std::string>("d3d9.forceAspectRatio",   "");
 

src/d3d9/d3d9_options.h

@@ -116,6 +116,9 @@ namespace dxvk {
     /// Always use a spec constant to determine sampler type (instead of just in PS 1.x)
     /// Works around a game bug in Halo CE where it gives cube textures to 2d/volume samplers
     bool forceSamplerTypeSpecConstants;
+
+    /// Forces an MSAA level on the swapchain
+    int32_t forceSwapchainMSAA;
   };
 
 }

src/d3d9/d3d9_swapchain.cpp

@@ -417,6 +417,12 @@ namespace dxvk {
 
     pPresentParams->BackBufferCount    = std::max(pPresentParams->BackBufferCount, 1u);
 
+    const int32_t forcedMSAA = m_parent->GetOptions()->forceSwapchainMSAA;
+    if (forcedMSAA != -1) {
+      pPresentParams->MultiSampleType    = D3DMULTISAMPLE_TYPE(forcedMSAA);
+      pPresentParams->MultiSampleQuality = 0;
+    }
+
     if (pPresentParams->Windowed) {
       GetWindowClientSize(pPresentParams->hDeviceWindow,
         pPresentParams->BackBufferWidth  ? nullptr : &pPresentParams->BackBufferWidth,