Fix banding artifacts in macOS viewer (#1977)

This addresses subtle banding on macOS with 10 bit / EDR displays.

I'm not a Metal expert and I suspect that the conversion code I added for screenshot saving could be improved (see commit comment), or ideally avoided (by saving to an HDR format such as EXR), but it gets the job done.

Author: shill-lucasfilm

source/MaterialXRenderMsl/CMakeLists.txt

@@ -59,7 +59,8 @@ elseif(APPLE)
     target_link_libraries(${TARGET_NAME}
             PUBLIC
             "-framework Foundation"
-            "-framework Metal")
+            "-framework Metal"
+            "-framework MetalPerformanceShaders")
 elseif(UNIX)
     target_link_libraries(${TARGET_NAME}
             PUBLIC

source/MaterialXRenderMsl/MetalFramebuffer.mm

@@ -81,7 +81,7 @@
                                         height:height
                                      mipmapped:NO];
         [texDescriptor setStorageMode:MTLStorageModePrivate];
-        [texDescriptor setUsage:MTLTextureUsageRenderTarget | MTLTextureUsageShaderRead];
+        [texDescriptor setUsage:MTLTextureUsageRenderTarget | MTLTextureUsageShaderRead | MTLTextureUsageShaderWrite];
 
         if (extColorTexture == nil)
         {

source/MaterialXRenderMsl/MetalState.h

@@ -43,7 +43,7 @@ struct MX_RENDERMSL_API MetalState
     void endEncoder();
     void endCommandBuffer();
 
-    void waitForComplition();
+    void waitForCompletion();
 
     MaterialX::MetalFramebufferPtr currentFramebuffer();
 

source/MaterialXRenderMsl/MetalState.mm

@@ -102,7 +102,7 @@
 
             MTLTileRenderPipelineDescriptor* renderPipelineDescriptor = [MTLTileRenderPipelineDescriptor new];
             [renderPipelineDescriptor setRasterSampleCount:1];
-            [[renderPipelineDescriptor colorAttachments][0] setPixelFormat:MTLPixelFormatBGRA8Unorm];
+            [[renderPipelineDescriptor colorAttachments][0] setPixelFormat:MTLPixelFormatRGBA16Float];
             [renderPipelineDescriptor setTileFunction:function];
             linearToSRGB_pso = [device newRenderPipelineStateWithTileDescriptor:renderPipelineDescriptor options:0 reflection:nil error:&error];
         }
@@ -171,7 +171,7 @@
         MTLRenderPipelineDescriptor* renderPipelineDesc = [MTLRenderPipelineDescriptor new];
         [renderPipelineDesc setVertexFunction:vertexfunction];
         [renderPipelineDesc setFragmentFunction:Fragmentfunction];
-        [[renderPipelineDesc colorAttachments][0] setPixelFormat:MTLPixelFormatBGRA8Unorm];
+        [[renderPipelineDesc colorAttachments][0] setPixelFormat:MTLPixelFormatRGBA16Float];
         [renderPipelineDesc setDepthAttachmentPixelFormat:MTLPixelFormatDepth32Float];
         linearToSRGB_pso = [device newRenderPipelineStateWithDescriptor:renderPipelineDesc error:&error];
     }
@@ -225,7 +225,7 @@
     [cmdBuffer waitUntilCompleted];
 }
 
-void MetalState::waitForComplition()
+void MetalState::waitForCompletion()
 {
     std::unique_lock<std::mutex> lock(inFlightMutex);
     while (inFlightCommandBuffers != 0)

source/MaterialXView/RenderPipelineMetal.mm

@@ -15,6 +15,8 @@
 
 #include <nanogui/messagedialog.h>
 
+#include <MetalPerformanceShaders/MetalPerformanceShaders.h>
+
 namespace
 {
 
@@ -59,10 +61,10 @@
                             MTL(device),
                             width * _viewer->m_pixel_ratio,
                             height * _viewer->m_pixel_ratio,
-                            4, mx::Image::BaseType::UINT8,
+                            4, mx::Image::BaseType::HALF,
                             MTL(supportsTiledPipeline) ?
                             (id<MTLTexture>)color_texture : nil,
-                            false,  MTLPixelFormatBGRA8Unorm));
+                            false, MTLPixelFormatRGBA16Float));
 }
 
 void MetalRenderPipeline::resizeFramebuffer(int width, int height,
@@ -697,16 +699,30 @@
     unsigned int width = MTL(currentFramebuffer())->getWidth();
     unsigned int height = MTL(currentFramebuffer())->getHeight();
 
-    MTL(waitForComplition());
+    MTL(waitForCompletion());
+
+    id<MTLTexture> srcTexture = MTL(supportsTiledPipeline) ?
+                                    (id<MTLTexture>)_viewer->_colorTexture :
+                                    MTL(currentFramebuffer())->getColorTexture();
+
     mx::MetalFramebufferPtr framebuffer = mx::MetalFramebuffer::create(
                             MTL(device),
                             width, height, 4,
                             mx::Image::BaseType::UINT8,
-                            MTL(supportsTiledPipeline) ?
-                                (id<MTLTexture>)_viewer->_colorTexture :
-                                MTL(currentFramebuffer())->getColorTexture(),
+                            nil,
                             false, MTLPixelFormatBGRA8Unorm);
-    mx::ImagePtr frame = framebuffer->getColorImage(MTL(cmdQueue));
+    id<MTLTexture> dstTexture = framebuffer->getColorTexture();
+
+    id<MTLCommandQueue> cmdQueue = MTL(cmdQueue);
+
+    // Copy with format conversion
+    MPSImageConversion* conversion = [[MPSImageConversion alloc] initWithDevice:MTL(device)];
+    id<MTLCommandBuffer> cmdBuffer = [cmdQueue commandBuffer];
+    [conversion encodeToCommandBuffer:cmdBuffer sourceTexture:srcTexture destinationTexture:dstTexture];
+    [cmdBuffer commit];
+    [cmdBuffer waitUntilCompleted];
+
+    mx::ImagePtr frame = framebuffer->getColorImage(cmdQueue);
 
     // Flips the captured image
     std::vector<unsigned char> tmp(frame->getRowStride());

source/MaterialXView/Viewer.cpp

@@ -52,6 +52,11 @@ const float DEFAULT_CAMERA_ZOOM = 1.0f;
 
 namespace
 {
+#ifdef MATERIALXVIEW_METAL_BACKEND
+const bool USE_FLOAT_BUFFER = true;
+#else
+const bool USE_FLOAT_BUFFER = false;
+#endif
 
 const int MIN_ENV_SAMPLE_COUNT = 4;
 const int MAX_ENV_SAMPLE_COUNT = 1024;
@@ -152,7 +157,7 @@ Viewer::Viewer(const std::string& materialFilename,
                int screenHeight,
                const mx::Color3& screenColor) :
     ng::Screen(ng::Vector2i(screenWidth, screenHeight), "MaterialXView",
-        true, false, true, true, false, 4, 0),
+        true, false, true, true, USE_FLOAT_BUFFER, 4, 0),
     _window(nullptr),
     _materialFilename(materialFilename),
     _meshFilename(meshFilename),