Merge #75

75: Use rasterizer discard r=kvark a=grovesNL

Stop setting the fragment shader and other states as stated in the spec when rasterizer discard is set. (Should anything else be disabled?)

Fixes segfaults in `dEQP-VK.api.descriptor_set.descriptor_set_layout_lifetime.graphics` on Metal (with gfx-rs/gfx#2035 fix)

Co-authored-by: Joshua Groves <josh@joshgroves.com>

libportability-gfx/src/impls.rs

@@ -1485,6 +1485,29 @@ pub extern "C" fn gfxCreateGraphicsPipelines(
     let mut cur_shader_stage = 0;
 
     let descs = infos.into_iter().map(|info| {
+        let (rasterizer, rasterizer_discard) = {
+            let state = unsafe { &*info.pRasterizationState };
+
+            let rasterizer = pso::Rasterizer {
+                polygon_mode: conv::map_polygon_mode(state.polygonMode, state.lineWidth),
+                cull_face: conv::map_cull_face(state.cullMode),
+                front_face: conv::map_front_face(state.frontFace),
+                depth_clamping: state.depthClampEnable == VK_TRUE,
+                depth_bias: if state.depthBiasEnable == VK_TRUE {
+                    Some(pso::DepthBias {
+                        const_factor: state.depthBiasConstantFactor,
+                        clamp: state.depthBiasClamp,
+                        slope_factor: state.depthBiasSlopeFactor,
+                    })
+                } else {
+                    None
+                },
+                conservative: false,
+            };
+
+            (rasterizer, state.rasterizerDiscardEnable == VK_TRUE)
+        };
+
         let shaders = {
             let mut set: pso::GraphicsShaderSet<_> = unsafe { mem::zeroed() };
 
@@ -1509,7 +1532,7 @@ pub extern "C" fn gfxCreateGraphicsPipelines(
                     VK_SHADER_STAGE_TESSELLATION_CONTROL_BIT => { set.hull = Some(entry_point); }
                     VK_SHADER_STAGE_TESSELLATION_EVALUATION_BIT => { set.domain = Some(entry_point); }
                     VK_SHADER_STAGE_GEOMETRY_BIT => { set.geometry = Some(entry_point); }
-                    VK_SHADER_STAGE_FRAGMENT_BIT => { set.fragment = Some(entry_point); }
+                    VK_SHADER_STAGE_FRAGMENT_BIT if !rasterizer_discard => { set.fragment = Some(entry_point); }
                     stage => panic!("Unexpected shader stage: {:?}", stage),
                 }
             }
@@ -1517,31 +1540,6 @@ pub extern "C" fn gfxCreateGraphicsPipelines(
             set
         };
 
-        let (rasterizer, rasterizer_discard) = {
-            let state = unsafe { &*info.pRasterizationState };
-
-            assert_eq!(state.rasterizerDiscardEnable, VK_FALSE); // TODO
-
-            let rasterizer = pso::Rasterizer {
-                polygon_mode: conv::map_polygon_mode(state.polygonMode, state.lineWidth),
-                cull_face: conv::map_cull_face(state.cullMode),
-                front_face: conv::map_front_face(state.frontFace),
-                depth_clamping: state.depthClampEnable == VK_TRUE,
-                depth_bias: if state.depthBiasEnable == VK_TRUE {
-                    Some(pso::DepthBias {
-                        const_factor: state.depthBiasConstantFactor,
-                        clamp: state.depthBiasClamp,
-                        slope_factor: state.depthBiasSlopeFactor,
-                    })
-                } else {
-                    None
-                },
-                conservative: false,
-            };
-
-            (rasterizer, state.rasterizerDiscardEnable == VK_TRUE)
-        };
-
         let (vertex_buffers, attributes) = {
             let input_state = unsafe { &*info.pVertexInputState };
 
@@ -1676,7 +1674,8 @@ pub extern "C" fn gfxCreateGraphicsPipelines(
 
         // TODO: `pDepthStencilState` could contain garbage, but implementations
         //        can ignore it in some circumstances. How to handle it?
-        let depth_stencil = unsafe { info
+        let depth_stencil = if !rasterizer_discard {
+            unsafe { info
                 .pDepthStencilState
                 .as_ref()
                 .map(|state| {
@@ -1718,27 +1717,36 @@ pub extern "C" fn gfxCreateGraphicsPipelines(
                         stencil: stencil_test,
                     }
                 })
+            }
+        } else {
+            None
         };
 
-        let vp_state = unsafe { &*info.pViewportState };
+        let vp_state = if !rasterizer_discard {
+            unsafe { info.pViewportState.as_ref() }
+        } else {
+            None
+        };
         let empty_dyn_states = [];
         let dyn_states = match unsafe { info.pDynamicState.as_ref() } {
-            Some(state) => unsafe {
+            Some(state) if !rasterizer_discard => unsafe {
                 slice::from_raw_parts(state.pDynamicStates, state.dynamicStateCount as _)
             },
-            None => &empty_dyn_states,
+            _ => &empty_dyn_states,
         };
         let baked_states = pso::BakedStates {
             viewport: if dyn_states.iter().any(|&ds| ds == VkDynamicState::VK_DYNAMIC_STATE_VIEWPORT) {
                 None
             } else {
-                unsafe { vp_state.pViewports.as_ref() }
+                vp_state
+                    .and_then(|vp| unsafe { vp.pViewports.as_ref() })
                     .map(conv::map_viewport)
             },
             scissor: if dyn_states.iter().any(|&ds| ds == VkDynamicState::VK_DYNAMIC_STATE_SCISSOR) {
                 None
             } else {
-                unsafe { vp_state.pScissors.as_ref() }
+                vp_state
+                    .and_then(|vp| unsafe { vp.pScissors.as_ref() })
                     .map(conv::map_rect)      
             },
             blend_color: if dyn_states.iter().any(|&ds| ds == VkDynamicState::VK_DYNAMIC_STATE_BLEND_CONSTANTS) {