From fdbc8079c96aabcd8350d1f4e18e450c9a9e456c Mon Sep 17 00:00:00 2001
From: Laszlo Agocs <laszlo.agocs@qt.io>
Date: Tue, 10 Jun 2025 12:01:13 +0200
Subject: [PATCH] rhi: Update the docs and manual test for geometry shaders

Task-number: QTBUG-137521
Change-Id: Ic9256eaaa55aef20c622429058fda9235c1f73c1
Reviewed-by: Andy Nichols <andy.nichols@qt.io>
---
 src/gui/rhi/qrhi.cpp                          |  21 +++++++-------
 .../rhi/geometryshader/buildshaders.bat       |   3 +-
 tests/manual/rhi/geometryshader/test.frag.qsb | Bin 456 -> 450 bytes
 tests/manual/rhi/geometryshader/test.geom     |   3 +-
 tests/manual/rhi/geometryshader/test.geom.qsb | Bin 1222 -> 1364 bytes
 tests/manual/rhi/geometryshader/test.vert     |   4 ++-
 tests/manual/rhi/geometryshader/test.vert.qsb | Bin 591 -> 665 bytes
 .../manual/rhi/geometryshader/test_geom.hlsl  |  26 ------------------
 8 files changed, 17 insertions(+), 40 deletions(-)
 delete mode 100644 tests/manual/rhi/geometryshader/test_geom.hlsl

diff --git a/src/gui/rhi/qrhi.cpp b/src/gui/rhi/qrhi.cpp
index 0628d07ce73..c47828120d8 100644
--- a/src/gui/rhi/qrhi.cpp
+++ b/src/gui/rhi/qrhi.cpp
@@ -936,16 +936,17 @@ Q_LOGGING_CATEGORY(QRHI_LOG_RUB, "qt.rhi.rub")
     avoided as it will not be supported by all backends. The maximum patch
     control point count portable between backends is 32.
 
-    \value GeometryShader Indicates that the geometry shader stage is
-    supported. When supported, a geometry shader can be specified in the
-    QRhiShaderStage list. Geometry Shaders are considered an experimental
-    feature in QRhi and can only be expected to be supported with Vulkan,
-    Direct 3D, OpenGL (3.2+) and OpenGL ES (3.2+), assuming the implementation
-    reports it as supported at run time. Geometry shaders have portability
-    issues between APIs, and therefore no guarantees can be given for a
-    universal solution. They will never be supported with Metal. Whereas with
-    Direct 3D a handwritten HLSL geometry shader must be injected into each
-    QShader for the geometry stage since qsb cannot generate this from SPIR-V.
+    \value GeometryShader Indicates that the geometry shader stage is supported.
+    When supported, a geometry shader can be specified in the QRhiShaderStage
+    list. Geometry Shaders are considered an experimental feature in QRhi and
+    can only be expected to be supported with Vulkan, Direct 3D 11 and 12,
+    OpenGL (3.2+) and OpenGL ES (3.2+), assuming the implementation reports it
+    as supported at run time. Starting with Qt 6.11 geometry shaders are
+    automatically translated to HLSL, and therefore no injection of handwritten
+    HLSL geometry shaders is necessary anymore (but note that gl_in and
+    expressions such as gl_in[0].gl_Position are not supported; rather, pass the
+    position as an output variable from the vertex shader). Geometry shaders are
+    not supported with Metal.
 
     \value TextureArrayRange Indicates that for
     \l{QRhi::newTextureArray()}{texture arrays} it is possible to specify a
diff --git a/tests/manual/rhi/geometryshader/buildshaders.bat b/tests/manual/rhi/geometryshader/buildshaders.bat
index a3b7296e168..c4ce5266429 100755
--- a/tests/manual/rhi/geometryshader/buildshaders.bat
+++ b/tests/manual/rhi/geometryshader/buildshaders.bat
@@ -1,6 +1,5 @@
 :: Copyright (C) 2024 The Qt Company Ltd.
 :: SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GPL-3.0-only WITH Qt-GPL-exception-1.0
 qsb --glsl 320es,410 --hlsl 50 test.vert -o test.vert.qsb
-qsb --glsl 320es,410 test.geom -o test.geom.qsb
-qsb -r hlsl,50,test_geom.hlsl test.geom.qsb
+qsb --glsl 320es,410 --hlsl 50 test.geom -o test.geom.qsb
 qsb --glsl 320es,410 --hlsl 50 test.frag -o test.frag.qsb
diff --git a/tests/manual/rhi/geometryshader/test.frag.qsb b/tests/manual/rhi/geometryshader/test.frag.qsb
index b6a5877b951c0f274ba3d1c1990fc83677cd8c02..b857f3629829ff98b25c709136d4180c1ce40538 100644
GIT binary patch
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diff --git a/tests/manual/rhi/geometryshader/test.geom b/tests/manual/rhi/geometryshader/test.geom
index 750a3085bd4..46f381f33a8 100644
--- a/tests/manual/rhi/geometryshader/test.geom
+++ b/tests/manual/rhi/geometryshader/test.geom
@@ -4,6 +4,7 @@
 
 layout(points) in;
 layout(line_strip, max_vertices = 7) out;
+layout(location = 0) in vec4 v_position[];
 
 layout(std140, binding = 0) uniform buf {
     float radius;
@@ -16,7 +17,7 @@ void main(void)
     {
         float theta = float(i) / 6.0f * 2.0 * M_PI;
 
-        gl_Position = gl_in[0].gl_Position;
+        gl_Position = v_position[0];
         gl_Position.xy += radius * vec2(cos(theta), sin(theta));
 
         EmitVertex();
diff --git a/tests/manual/rhi/geometryshader/test.geom.qsb b/tests/manual/rhi/geometryshader/test.geom.qsb
index 9aa4a0cf98eb4f084f8f717d3fc59776f8cbe130..93a059b502f3711e067a059bc3b0402cc59db22e 100644
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diff --git a/tests/manual/rhi/geometryshader/test.vert b/tests/manual/rhi/geometryshader/test.vert
index af06581f6a4..33c52df4e64 100644
--- a/tests/manual/rhi/geometryshader/test.vert
+++ b/tests/manual/rhi/geometryshader/test.vert
@@ -1,8 +1,10 @@
 #version 440
 
 layout(location = 0) in vec3 position;
+layout(location = 0) out vec4 v_position;
 
 void main()
 {
-    gl_Position = vec4(position, 1.0);
+    v_position = vec4(position, 1.0);
+    gl_Position = v_position;
 }
diff --git a/tests/manual/rhi/geometryshader/test.vert.qsb b/tests/manual/rhi/geometryshader/test.vert.qsb
index 7238d8037b66db246743ca0ddd23b39a4faea13f..4b12cd37d0c3af1b8fa72625aae5d2a2941b26b0 100644
GIT binary patch
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diff --git a/tests/manual/rhi/geometryshader/test_geom.hlsl b/tests/manual/rhi/geometryshader/test_geom.hlsl
deleted file mode 100644
index e58659252b1..00000000000
--- a/tests/manual/rhi/geometryshader/test_geom.hlsl
+++ /dev/null
@@ -1,26 +0,0 @@
-struct VertexOutput
-{
-    float4 position : SV_Position;
-};
-
-struct PixelInput
-{
-    float4 position : SV_POSITION;
-};
-
-cbuffer buf : register(b0)
-{
-    float radius : packoffset(c0);
-};
-
-[maxvertexcount(7)]
-void main(point VertexOutput input[1], inout LineStream<PixelInput> OutputStream)
-{
-    PixelInput output;
-    for (int i = 0; i < 7; ++i) {
-        float theta = float(i) / 6.0f * 2.0 * 3.14159265;
-        output.position = input[0].position;
-        output.position.xy += radius * float2(cos(theta), sin(theta));
-        OutputStream.Append(output);
-    }
-}