From 3b8e489b6f384239cbe30a2dccc064a4ecc2c9bd Mon Sep 17 00:00:00 2001
From: Vlad Zahorodnii <vlad.zahorodnii@kde.org>
Date: Mon, 12 Oct 2020 23:56:07 +0300
Subject: [PATCH] platforms/drm: Compute correct cursor transform matrix

Currently, when the DRM platform uses cursor planes, the cursor on
a rotated output may be cropped because the math behind the current
cursor transform matrix is off.

In order to fix the cropping issue, this change replaces the current
cursor transform matrix with the core part of the surface-to-buffer
matrix, which was written against the wl_output spec.

BUG: 427605
CCBUG: 427060
---
 plugins/platforms/drm/drm_output.cpp | 50 ++++++++++++++++++++++------
 plugins/platforms/drm/drm_output.h   |  1 -
 2 files changed, 39 insertions(+), 12 deletions(-)

diff --git a/plugins/platforms/drm/drm_output.cpp b/plugins/platforms/drm/drm_output.cpp
index 8d081d8e2d..8a27f41880 100644
--- a/plugins/platforms/drm/drm_output.cpp
+++ b/plugins/platforms/drm/drm_output.cpp
@@ -133,18 +133,45 @@ bool DrmOutput::showCursor()
     return ret;
 }
 
-QMatrix4x4 DrmOutput::matrixDisplay(const QSize &s) const
+static QMatrix4x4 matrixForTransform(const QRectF &rect, qreal scale, DrmOutput::Transform transform)
 {
     QMatrix4x4 matrix;
-    const int angle = rotation();
-    if (angle) {
-        const QSize center = s / 2;
 
-        matrix.translate(center.width(), center.height());
-        matrix.rotate(-angle, 0, 0, 1);
-        matrix.translate(-center.width(), -center.height());
+    matrix.scale(scale);
+
+    switch (transform) {
+    case DrmOutput::Transform::Normal:
+    case DrmOutput::Transform::Flipped:
+        break;
+    case DrmOutput::Transform::Rotated90:
+    case DrmOutput::Transform::Flipped90:
+        matrix.translate(0, rect.width());
+        matrix.rotate(-90, 0, 0, 1);
+        break;
+    case DrmOutput::Transform::Rotated180:
+    case DrmOutput::Transform::Flipped180:
+        matrix.translate(rect.width(), rect.height());
+        matrix.rotate(-180, 0, 0, 1);
+        break;
+    case DrmOutput::Transform::Rotated270:
+    case DrmOutput::Transform::Flipped270:
+        matrix.translate(rect.height(), 0);
+        matrix.rotate(-270, 0, 0, 1);
+        break;
     }
-    matrix.scale(scale());
+
+    switch (transform) {
+    case DrmOutput::Transform::Flipped:
+    case DrmOutput::Transform::Flipped180:
+    case DrmOutput::Transform::Flipped90:
+    case DrmOutput::Transform::Flipped270:
+        matrix.translate(rect.width(), 0);
+        matrix.scale(-1, 1);
+        break;
+    default:
+        break;
+    }
+
     return matrix;
 }
 
@@ -163,15 +190,13 @@ void DrmOutput::updateCursor()
 
     QPainter p;
     p.begin(c);
-    p.setWorldTransform(matrixDisplay(QSize(cursorImage.width(), cursorImage.height())).toTransform());
+    p.setWorldTransform(matrixForTransform(cursorImage.rect(), scale(), transform()).toTransform());
     p.drawImage(QPoint(0, 0), cursorImage);
     p.end();
 }
 
 void DrmOutput::moveCursor(Cursor *cursor, const QPoint &globalPos)
 {
-    const QMatrix4x4 hotspotMatrix = matrixDisplay(cursor->image().size());
-
     const QPoint localPos = globalPos - AbstractWaylandOutput::globalPos();
     QPoint pos = localPos;
 
@@ -197,7 +222,10 @@ void DrmOutput::moveCursor(Cursor *cursor, const QPoint &globalPos)
         Q_UNREACHABLE();
     }
     pos *= scale();
+
+    const QMatrix4x4 hotspotMatrix = matrixForTransform(cursor->image().rect(), scale(), transform());
     pos -= hotspotMatrix.map(cursor->hotspot());
+
     drmModeMoveCursor(m_gpu->fd(), m_crtc->id(), pos.x(), pos.y());
 }
 
diff --git a/plugins/platforms/drm/drm_output.h b/plugins/platforms/drm/drm_output.h
index 7220c3152b..923eba5456 100644
--- a/plugins/platforms/drm/drm_output.h
+++ b/plugins/platforms/drm/drm_output.h
@@ -142,7 +142,6 @@ private:
 
     int gammaRampSize() const override;
     bool setGammaRamp(const GammaRamp &gamma) override;
-    QMatrix4x4 matrixDisplay(const QSize &s) const;
 
     DrmBackend *m_backend;
     DrmGpu *m_gpu;