Clarify the front face winding order in the Vulkan examples

After applying the correction matrix the front face is CW, not CCW.

The examples work either way but fix them up to avoid reader confusion.

Change-Id: I491e6dc17c21897a59f36d32061e937f2b6c4c9d
Reviewed-by: Andy Nichols <[email protected]>

3 files changed, 7 insertions, 3 deletions

diff --git a/examples/vulkan/hellovulkantexture/hellovulkantexture.cpp b/examples/vulkan/hellovulkantexture/hellovulkantexture.cpp
index 9953352e28c..5e52d5e006f 100644
--- a/examples/vulkan/hellovulkantexture/hellovulkantexture.cpp
+++ b/examples/vulkan/hellovulkantexture/hellovulkantexture.cpp
@@ -612,8 +612,8 @@ void VulkanRenderer::initResources()
     memset(&rs, 0, sizeof(rs));
     rs.sType = VK_STRUCTURE_TYPE_PIPELINE_RASTERIZATION_STATE_CREATE_INFO;
     rs.polygonMode = VK_POLYGON_MODE_FILL;
-    rs.cullMode = VK_CULL_MODE_NONE; // we want the back face as well
-    rs.frontFace = VK_FRONT_FACE_COUNTER_CLOCKWISE;
+    rs.cullMode = VK_CULL_MODE_BACK_BIT;
+    rs.frontFace = VK_FRONT_FACE_CLOCKWISE;
     rs.lineWidth = 1.0f;
     pipelineInfo.pRasterizationState = &rs;
 
diff --git a/examples/vulkan/shared/trianglerenderer.cpp b/examples/vulkan/shared/trianglerenderer.cpp
index f2e636bbe61..a0800080a06 100644
--- a/examples/vulkan/shared/trianglerenderer.cpp
+++ b/examples/vulkan/shared/trianglerenderer.cpp
@@ -337,7 +337,7 @@ void TriangleRenderer::initResources()
     rs.sType = VK_STRUCTURE_TYPE_PIPELINE_RASTERIZATION_STATE_CREATE_INFO;
     rs.polygonMode = VK_POLYGON_MODE_FILL;
     rs.cullMode = VK_CULL_MODE_NONE; // we want the back face as well
-    rs.frontFace = VK_FRONT_FACE_COUNTER_CLOCKWISE;
+    rs.frontFace = VK_FRONT_FACE_CLOCKWISE;
     rs.lineWidth = 1.0f;
     pipelineInfo.pRasterizationState = &rs;
 
diff --git a/src/gui/vulkan/qvulkanwindow.cpp b/src/gui/vulkan/qvulkanwindow.cpp
index d5af71cd4be..b158fa7e942 100644
--- a/src/gui/vulkan/qvulkanwindow.cpp
+++ b/src/gui/vulkan/qvulkanwindow.cpp
@@ -2692,6 +2692,10 @@ QImage QVulkanWindow::grab()
    without any further corrections to the vertex Z positions, while using the
    projection matrices retrieved from the QMatrix4x4 functions, such as
    QMatrix4x4::perspective(), as-is.
+
+   \note With vertex data following the default OpenGL rules (that is, the
+   front face being CCW), the correct winding order in the rasterization state
+   after applying this matrix is clockwise (\c{VK_FRONT_FACE_CLOCKWISE}).
  */
 const QMatrix4x4 *QVulkanWindow::clipCorrectionMatrix()
 {