Fix: NativeRendering text for non-integer screen scaling

Commit 6e883c53 introduced snapping to pixel grid for non-integer
device pixel ratios. But the snapping also modified the w element of
the coord vector, which resulted in mangled and offset rendering.

As a driveby, add the dpr snapping also to the outlinetext shader, as
it improves rendering quality.

Fixes: QTBUG-70481
Fixes: QTBUG-78160
Change-Id: I4c4b1788005514adc0255878ba24cdf1acc6755f
Reviewed-by: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>

7 files changed, 51 insertions, 6 deletions

diff --git a/src/quick/scenegraph/shaders/outlinedtext.vert b/src/quick/scenegraph/shaders/outlinedtext.vert
index ced8afd034..9df832de3c 100644
--- a/src/quick/scenegraph/shaders/outlinedtext.vert
+++ b/src/quick/scenegraph/shaders/outlinedtext.vert
@@ -1,6 +1,7 @@
 uniform highp mat4 matrix;
 uniform highp vec2 textureScale;
 uniform highp vec2 shift;
+uniform highp float dpr;
 
 attribute highp vec4 vCoord;
 attribute highp vec2 tCoord;
@@ -18,5 +19,6 @@ void main()
      sCoordDown = (tCoord - vec2(0.0, 1.0)) * textureScale;
      sCoordLeft = (tCoord - vec2(-1.0, 0.0)) * textureScale;
      sCoordRight = (tCoord - vec2(1.0, 0.0)) * textureScale;
-     gl_Position = matrix * vCoord;
+     vec3 dprSnapPos = floor(vCoord.xyz * dpr + 0.5) / dpr;
+     gl_Position = matrix * vec4(dprSnapPos, vCoord.w);
 }
\ No newline at end of file
diff --git a/src/quick/scenegraph/shaders/outlinedtext_core.vert b/src/quick/scenegraph/shaders/outlinedtext_core.vert
index 4aa13101fd..ae945b013a 100644
--- a/src/quick/scenegraph/shaders/outlinedtext_core.vert
+++ b/src/quick/scenegraph/shaders/outlinedtext_core.vert
@@ -12,6 +12,7 @@ out vec2 sCoordRight;
 uniform mat4 matrix;
 uniform vec2 textureScale;
 uniform vec2 shift;
+uniform float dpr;
 
 void main()
 {
@@ -20,5 +21,6 @@ void main()
      sCoordDown = (tCoord - vec2(0.0, 1.0)) * textureScale;
      sCoordLeft = (tCoord - vec2(-1.0, 0.0)) * textureScale;
      sCoordRight = (tCoord - vec2(1.0, 0.0)) * textureScale;
-     gl_Position = matrix * vCoord;
+     vec3 dprSnapPos = round(vCoord.xyz * dpr + 0.5) / dpr;
+     gl_Position = matrix * vec4(dprSnapPos, vCoord.w);
 }
\ No newline at end of file
diff --git a/src/quick/scenegraph/shaders/styledtext.vert b/src/quick/scenegraph/shaders/styledtext.vert
index 7001bbc262..29c9902609 100644
--- a/src/quick/scenegraph/shaders/styledtext.vert
+++ b/src/quick/scenegraph/shaders/styledtext.vert
@@ -13,5 +13,6 @@ void main()
 {
      sampleCoord = tCoord * textureScale;
      shiftedSampleCoord = (tCoord - shift) * textureScale;
-     gl_Position = matrix * floor(vCoord * dpr + 0.5) / dpr;
+     vec3 dprSnapPos = floor(vCoord.xyz * dpr + 0.5) / dpr;
+     gl_Position = matrix * vec4(dprSnapPos, vCoord.w);
 }
diff --git a/src/quick/scenegraph/shaders/styledtext_core.vert b/src/quick/scenegraph/shaders/styledtext_core.vert
index c522877bb3..7e313eb797 100644
--- a/src/quick/scenegraph/shaders/styledtext_core.vert
+++ b/src/quick/scenegraph/shaders/styledtext_core.vert
@@ -15,5 +15,6 @@ void main()
 {
      sampleCoord = tCoord * textureScale;
      shiftedSampleCoord = (tCoord - shift) * textureScale;
-     gl_Position = matrix * round(vCoord * dpr) / dpr;
+     vec3 dprSnapPos = round(vCoord.xyz * dpr + 0.5) / dpr;
+     gl_Position = matrix * vec4(dprSnapPos, vCoord.w);
 }
diff --git a/src/quick/scenegraph/shaders/textmask.vert b/src/quick/scenegraph/shaders/textmask.vert
index 4c678270d0..1692159d2c 100644
--- a/src/quick/scenegraph/shaders/textmask.vert
+++ b/src/quick/scenegraph/shaders/textmask.vert
@@ -10,5 +10,6 @@ varying highp vec2 sampleCoord;
 void main()
 {
      sampleCoord = tCoord * textureScale;
-     gl_Position = matrix * floor(vCoord * dpr + 0.5) / dpr;
+     vec3 dprSnapPos = floor(vCoord.xyz * dpr + 0.5) / dpr;
+     gl_Position = matrix * vec4(dprSnapPos, vCoord.w);
 }
diff --git a/src/quick/scenegraph/shaders/textmask_core.vert b/src/quick/scenegraph/shaders/textmask_core.vert
index f996040f70..5c510a2d23 100644
--- a/src/quick/scenegraph/shaders/textmask_core.vert
+++ b/src/quick/scenegraph/shaders/textmask_core.vert
@@ -12,5 +12,6 @@ uniform float dpr;
 void main()
 {
      sampleCoord = tCoord * textureScale;
-     gl_Position = matrix * round(vCoord * dpr) / dpr;
+     vec3 dprSnapPos = round(vCoord.xyz * dpr + 0.5) / dpr;
+     gl_Position = matrix * vec4(dprSnapPos, vCoord.w);
 }
diff --git a/tests/manual/scenegraph_lancelot/data/text/text_style2.qml b/tests/manual/scenegraph_lancelot/data/text/text_style2.qml
new file mode 100644
index 0000000000..984ca6a1ed
--- /dev/null
+++ b/tests/manual/scenegraph_lancelot/data/text/text_style2.qml
@@ -0,0 +1,37 @@
+import QtQuick 2.0
+
+//vary font style
+
+Item {
+    width: 320
+    height: 480
+
+    Column {
+        anchors.fill: parent
+        Repeater {
+            model: [Text.Normal, Text.Outline, Text.Raised, Text.Sunken]
+            Text {
+                renderType: Text.QtRendering
+                width: parent.width
+                wrapMode: Text.Wrap
+                font.pointSize: 10
+                style: modelData
+                styleColor: "green"
+                text: "The quick fox jumps in style " + modelData
+            }
+        }
+
+        Repeater {
+            model: [Text.Normal, Text.Outline, Text.Raised, Text.Sunken]
+            Text {
+                renderType: Text.NativeRendering
+                width: parent.width
+                wrapMode: Text.Wrap
+                font.pointSize: 10
+                style: modelData
+                styleColor: "green"
+                text: "The quick fox jumps in style " + modelData
+            }
+        }
+    }
+}