[systemsettings] [Bug 336089] Font preview - rendering problem

[Thomas Lübking via KDE Bugzilla]

https://bugs.kde.org/show_bug.cgi?id=336089

--- Comment #51 from Thomas Lübking <thomas.luebk...@gmail.com> ---
Thanks a lot. Risking to be a complete PITA, mind testing this patch and
notably watching on whether you're on 32bit depth and whether a format is found
(and it's the correct one ;-)


diff --git a/kcms/kfontinst/lib/FcEngine.cpp b/kcms/kfontinst/lib/FcEngine.cpp
index 19b7206..6026753 100644
--- a/kcms/kfontinst/lib/FcEngine.cpp
+++ b/kcms/kfontinst/lib/FcEngine.cpp
@@ -219,6 +219,7 @@ class CFcEngine::Xft
     XftColor itsTxtColor,
              itsBgndColor;
     Pix      itsPix;
+    QImage::Format imageFormat;
 };

 CFcEngine::Xft::Xft()
@@ -267,6 +268,47 @@ bool CFcEngine::Xft::init(const QColor &txt, const QColor
&bnd, int w, int h)
         XftColorAllocValue(QX11Info::display(), visual, colorMap, &xrenderCol,
&itsTxtColor);
     }

+    XVisualInfo defaultVinfo;
+    defaultVinfo.depth = DefaultDepth(QX11Info::display(), 0);
+    // normal/failsafe
+    imageFormat = QImage::Format_RGB32; // 24bit
+    switch (defaultVinfo.depth) {
+        case 32: imageFormat = QImage::Format_ARGB32_Premultiplied; break;
+        case 30: imageFormat = QImage::Format_RGB30; break;
+        case 16: imageFormat = QImage::Format_RGB16; break;
+        case 8: imageFormat = QImage::Format_Grayscale8; break;
+        default: break;
+    }
+    qDebug() << "Depth" << defaultVinfo.depth;
+    if (defaultVinfo.depth == 30 || defaultVinfo.depth == 32) {
+        // detect correct format
+        int num_vinfo = 0;
+        defaultVinfo.visual = DefaultVisual(QX11Info::display(), 0);
+        defaultVinfo.screen = 0;
+        defaultVinfo.visualid = XVisualIDFromVisual(defaultVinfo.visual);
+        XVisualInfo *vinfo = XGetVisualInfo(QX11Info::display(),
VisualIDMask|VisualScreenMask|VisualDepthMask, &defaultVinfo, &num_vinfo);
+        for (int i = 0; i < num_vinfo; ++i) {
+            if (vinfo[i].visual == defaultVinfo.visual) {
+                if (defaultVinfo.depth == 30) {
+                    if (vinfo[i].red_mask == 0x3ff)
+                        imageFormat = QImage::Format_BGR30;
+                    else if (vinfo[i].blue_mask == 0x3ff)
+                        imageFormat = QImage::Format_RGB30;
+                } else if (defaultVinfo.depth == 32) {
+                    if (vinfo[i].blue_mask == 0xff)
+                        imageFormat = QImage::Format_ARGB32_Premultiplied;
+                    else if (vinfo[i].red_mask == 0x3ff)
+                        imageFormat = QImage::Format_A2BGR30_Premultiplied;
+                    else if (vinfo[i].blue_mask == 0x3ff)
+                        imageFormat = QImage::Format_A2RGB30_Premultiplied;
+                }
+                qDebug() << "Found one" << imageFormat;
+                break;
+            }
+        }
+        XFree(vinfo);
+    }
+
     if(itsPix.allocate(w, h) && itsDraw)
         XftDrawChange(itsDraw, itsPix.x11);

@@ -537,7 +579,7 @@ QImage CFcEngine::Xft::toImage(int w, int h) const
     if (!xImage) {
         return QImage();
     }
-    return QImage(xImage->data, xImage->width, xImage->height, xImage->stride,
QImage::Format_ARGB32_Premultiplied, &cleanupXImage, xImage);
+    return QImage(xImage->data, xImage->width, xImage->height, xImage->stride,
imageFormat, &cleanupXImage, xImage);
 }

 inline int point2Pixel(int point)

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