Make QQuickFbo work with the OpenGL backend of QRhi

So no matter if Quick goes directly to OpenGL, or via QRhi,
QQuickFramebufferObject will still work.

Also fix up the fboitem example to use a ShaderEffect that works with
both rendering paths.

With graphics APIs other than OpenGL the item will be empty, as QQuickFbo
is not something we can support there.

Task-number: QTBUG-79222
Change-Id: I52177d3a75f619f7075a2fc829573c17031eded1
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

5 files changed, 39 insertions, 14 deletions

diff --git a/examples/quick/scenegraph/fboitem/fboitem.qrc b/examples/quick/scenegraph/fboitem/fboitem.qrc
index 9d9db70654..eeb5c36afd 100644
--- a/examples/quick/scenegraph/fboitem/fboitem.qrc
+++ b/examples/quick/scenegraph/fboitem/fboitem.qrc
@@ -1,5 +1,7 @@
 <RCC>
     <qresource prefix="/scenegraph/fboitem">
         <file>main.qml</file>
+        <file>shaders/checker.frag</file>
+        <file>shaders/+qsb/checker.frag</file>
     </qresource>
 </RCC>
diff --git a/examples/quick/scenegraph/fboitem/main.qml b/examples/quick/scenegraph/fboitem/main.qml
index 92fa99e847..1f1829deda 100644
--- a/examples/quick/scenegraph/fboitem/main.qml
+++ b/examples/quick/scenegraph/fboitem/main.qml
@@ -67,20 +67,7 @@ Item {
 
         property size pixelSize: Qt.size(width / tileSize, height / tileSize);
 
-        fragmentShader:
-            "
-            uniform lowp vec4 color1;
-            uniform lowp vec4 color2;
-            uniform highp vec2 pixelSize;
-            varying highp vec2 qt_TexCoord0;
-            void main() {
-                highp vec2 tc = sign(sin(3.14159265358979323846 * qt_TexCoord0 * pixelSize));
-                if (tc.x != tc.y)
-                    gl_FragColor = color1;
-                else
-                    gl_FragColor = color2;
-            }
-            "
+        fragmentShader: "qrc:/scenegraph/fboitem/shaders/checker.frag"
     }
 
     Renderer {
diff --git a/examples/quick/scenegraph/fboitem/shaders/+qsb/checker.frag b/examples/quick/scenegraph/fboitem/shaders/+qsb/checker.frag
new file mode 100644
index 0000000000..5037899d19
--- /dev/null
+++ b/examples/quick/scenegraph/fboitem/shaders/+qsb/checker.frag
diff --git a/examples/quick/scenegraph/fboitem/shaders/checker.frag b/examples/quick/scenegraph/fboitem/shaders/checker.frag
new file mode 100644
index 0000000000..044b3bad58
--- /dev/null
+++ b/examples/quick/scenegraph/fboitem/shaders/checker.frag
@@ -0,0 +1,14 @@
+uniform lowp vec4 color1;
+uniform lowp vec4 color2;
+uniform highp vec2 pixelSize;
+
+varying highp vec2 qt_TexCoord0;
+
+void main()
+{
+    highp vec2 tc = sign(sin(3.14159265358979323846 * qt_TexCoord0 * pixelSize));
+    if (tc.x != tc.y)
+        gl_FragColor = color1;
+    else
+        gl_FragColor = color2;
+}
diff --git a/examples/quick/scenegraph/fboitem/shaders/checker_rhi.frag b/examples/quick/scenegraph/fboitem/shaders/checker_rhi.frag
new file mode 100644
index 0000000000..1e4131d026
--- /dev/null
+++ b/examples/quick/scenegraph/fboitem/shaders/checker_rhi.frag
@@ -0,0 +1,22 @@
+#version 440
+
+layout(std140, binding = 0) uniform buf {
+    mat4 qt_Matrix;
+    float qt_Opacity;
+
+    vec4 color1;
+    vec4 color2;
+    vec2 pixelSize;
+} ubuf;
+
+layout(location = 0) in vec2 qt_TexCoord0;
+layout(location = 0) out vec4 fragColor;
+
+void main()
+{
+    vec2 tc = sign(sin(3.14159265358979323846 * qt_TexCoord0 * ubuf.pixelSize));
+    if (tc.x != tc.y)
+        fragColor = ubuf.color1;
+    else
+        fragColor = ubuf.color2;
+}