Merge #3500

3500: [vk] fix viewport/scissor count validation error r=kvark a=kvark

Fixes this VU reported in gfx-rs/wgpu#1059 :
> [0.375320 ERROR]()(no module):
VALIDATION [VUID-VkPipelineViewportStateCreateInfo-viewportCount-01216 (-376016417)] : Validation Error: [ VUID-VkPipelineViewportStateCreateInfo-viewportCount-01216 ] Object 0: handle = 0x2d93dbcf100, type = VK_OBJECT_TYPE_DEVICE; | MessageID = 0xe99671df | vkCreateGraphicsPipelines: The VkPhysicalDeviceFeatures::multiViewport feature is disabled, but pCreateInfos[0].pViewportState->viewportCount (=0) is not 1. The Vulkan spec states: If the multiple viewports feature is not enabled, viewportCount must be 1 (https://vulkan.lunarg.com/doc/view/1.2.141.0/windows/1.2-extensions/vkspec.html#VUID-VkPipelineViewportStateCreateInfo-viewportCount-01216)
object info: (type: DEVICE, hndl: 3132066951424)

PR checklist:
- [x] `make` succeeds (on *nix)
- [ ] `make reftests` succeeds
- [x] tested on wgpu-rs examples


Co-authored-by: Dzmitry Malyshau <dmalyshau@mozilla.com>

src/backend/vulkan/src/device.rs

@@ -54,8 +54,8 @@ struct GraphicsPipelineInfoBuf {
     depth_stencil_state: vk::PipelineDepthStencilStateCreateInfo,
     color_blend_state: vk::PipelineColorBlendStateCreateInfo,
     pipeline_dynamic_state: vk::PipelineDynamicStateCreateInfo,
-    viewport: vk::Viewport,
-    scissor: vk::Rect2D,
+    viewports: [vk::Viewport; 1],
+    scissors: [vk::Rect2D; 1],
 }
 impl GraphicsPipelineInfoBuf {
     unsafe fn add_stage<'a>(
@@ -256,36 +256,30 @@ impl GraphicsPipelineInfoBuf {
         };
 
         this.viewport_state = {
-            let scissors = match desc.baked_states.scissor {
+            //Note: without `multiViewport` feature, there has to be
+            // the count of 1 for both viewports and scissors, even
+            // though the actual pointers are ignored.
+            match desc.baked_states.scissor {
                 Some(ref rect) => {
-                    this.scissor = conv::map_rect(rect);
-                    Some([this.scissor])
+                    this.scissors = [conv::map_rect(rect)];
                 }
                 None => {
                     this.dynamic_states.push(vk::DynamicState::SCISSOR);
-                    None
                 }
-            };
-            let viewports = match desc.baked_states.viewport {
+            }
+            match desc.baked_states.viewport {
                 Some(ref vp) => {
-                    this.viewport = device.shared.map_viewport(vp);
-                    Some([this.viewport])
+                    this.viewports = [device.shared.map_viewport(vp)];
                 }
                 None => {
                     this.dynamic_states.push(vk::DynamicState::VIEWPORT);
-                    None
                 }
-            };
-
-            let mut builder = vk::PipelineViewportStateCreateInfo::builder()
-                .flags(vk::PipelineViewportStateCreateFlags::empty());
-            if let Some(scissors) = &scissors {
-                builder = builder.scissors(scissors);
             }
-            if let Some(viewports) = &viewports {
-                builder = builder.viewports(viewports);
-            }
-            builder.build()
+            vk::PipelineViewportStateCreateInfo::builder()
+                .flags(vk::PipelineViewportStateCreateFlags::empty())
+                .scissors(&this.scissors)
+                .viewports(&this.viewports)
+                .build()
         };
 
         this.multisample_state = match desc.multisampling {