Vulkan : Fix maxVertexOutputComponents

GL_MAX_VERTEX_OUTPUT_COMPONENTS should mirror Vulkan's
reported maxVertexOutputComponents; this shouldn't include
any gl_Position adjustments. It was previously set as
maxVaryingVectors * 4.

The workaround for AMD that reserved an extra varying
due to driver instability is no longer required (see:
https://chromium-review.googlesource.com/c/angle/angle/+/1980272)

Bug: angleproject:4233
Change-Id: I8d7b8eafa7edd4c56005dad039fe69e072692fca
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1975851
Commit-Queue: Shahbaz Youssefi <[email protected]>
Reviewed-by: Jamie Madill <[email protected]>

Author: gary-sweet

src/libANGLE/renderer/vulkan/vk_caps_utils.cpp

@@ -427,14 +427,11 @@ void RendererVk::ensureCapsInitialized() const
     // The gles2.0 section 2.10 states that "gl_Position is not a varying variable and does
     // not count against this limit.", but the Vulkan spec has no such mention in its Built-in
     // vars section. It is implicit that we need to actually reserve it for Vulkan in that case.
-    //
-    // Note: AMD has a weird behavior when we edge toward the maximum number of varyings and can
-    // often crash. Reserving an additional varying just for them bringing the total to 2.
-    constexpr GLint kReservedVaryingCount = 2;
-    mNativeCaps.maxVaryingVectors =
-        LimitToInt((limitsVk.maxVertexOutputComponents / 4) - kReservedVaryingCount);
-    mNativeCaps.maxVertexOutputComponents =
-        LimitToInt(static_cast<uint32_t>(mNativeCaps.maxVaryingVectors * 4));
+    GLint reservedVaryingVectorCount = 1;
+
+    mNativeCaps.maxVaryingVectors = LimitToInt(
+        (limitsVk.maxVertexOutputComponents / kComponentsPerVector) - reservedVaryingVectorCount);
+    mNativeCaps.maxVertexOutputComponents = LimitToInt(limitsVk.maxVertexOutputComponents);
 
     mNativeCaps.maxTransformFeedbackInterleavedComponents =
         gl::IMPLEMENTATION_MAX_TRANSFORM_FEEDBACK_INTERLEAVED_COMPONENTS;