android: Workaround display refresh bug

Whenever the screen has a non-zero offset, there is a display refresh
bug that shows up on the simulator, where the leftmost pixels of the
screen are refreshed with a delay. This seems to be a compositor bug,
but the only workaround I found after half a day of trying was to have
a larger pixmap that covers the whole screen width.

Signed-off-by: Christophe de Dinechin <christophe@dinechin.org>

Author: c3d

sim/sim-screen.cpp

@@ -80,6 +80,8 @@ SimScreen::SimScreen(QWidget *parent)
       bgPen(bgColor),
       fgPen(fgColor),
       mainPixmap(SIM_LCD_W, SIM_LCD_H),
+      pixmapWidth(SIM_LCD_W),
+      contentXOffset(0),
       redraws(0)
 {
     screen.clear();
@@ -112,6 +114,45 @@ SimScreen::~SimScreen()
 }
 
 
+void SimScreen::setPixmapGeometry(int totalWidth, int xOffset)
+// ----------------------------------------------------------------------------
+//   Set the pixmap geometry for Android (wider pixmap with black bars)
+// ----------------------------------------------------------------------------
+{
+    // Ensure pixmap is wide enough to contain LCD content and black bars
+    int requiredWidth = xOffset + SIM_LCD_W;
+    if (totalWidth < requiredWidth)
+        totalWidth = requiredWidth;
+
+    if (totalWidth != pixmapWidth || xOffset != contentXOffset)
+    {
+        pixmapWidth = totalWidth;
+        contentXOffset = xOffset;
+
+        // Create a new wider pixmap filled with black bars
+        QPixmap newPixmap(pixmapWidth, SIM_LCD_H);
+        newPixmap.fill(Qt::black);
+
+        // Draw the LCD content area with the background color
+        QPainter painter(&newPixmap);
+        painter.fillRect(contentXOffset, 0, SIM_LCD_W, SIM_LCD_H, bgColor);
+        painter.end();
+
+        // Replace the pixmap
+        mainPixmap = newPixmap;
+        mainScreen->setPixmap(mainPixmap);
+
+        // Update scene rect to match new pixmap width
+        setSceneRect(0, 0, pixmapWidth, screen_height);
+        centerOn(qreal(pixmapWidth) / 2, qreal(screen_height) / 2);
+
+        // Force redraw of all LCD content
+        for (size_t i = 0; i < sizeof(lcd_copy) / sizeof(*lcd_copy); i++)
+            lcd_copy[i] = ~lcd_buffer[i];
+    }
+}
+
+
 void SimScreen::setScale(qreal sf)
 // ----------------------------------------------------------------------------
 //   Adjust the scaling factor
@@ -135,6 +176,10 @@ void SimScreen::updatePixmap()
 {
     // Monochrome screen
     QPainter pt(&mainPixmap);
+#ifdef ANDROID
+    // On Android, set clip rect to only allow drawing in the LCD content area
+    pt.setClipRect(contentXOffset, 0, SIM_LCD_W, SIM_LCD_H);
+#endif
     pixword mask = ~(~0U << color::BPP);
     surface s(lcd_buffer, LCD_W, LCD_H, LCD_SCANLINE, LCD_W);
     for (int y = 0; y < SIM_LCD_H; y++)
@@ -161,7 +206,11 @@ void SimScreen::updatePixmap()
                         coord yy = y;
                         s.horizontal_adjust(xx, xx);
                         s.vertical_adjust(yy, yy);
+#ifdef ANDROID
+                        pt.drawPoint(xx + contentXOffset, yy);
+#else
                         pt.drawPoint(xx, yy);
+#endif
                     }
                 }
                 lcd_copy[woffs] = lcd_buffer[woffs];

sim/sim-screen.h

@@ -57,21 +57,24 @@ class SimScreen : public QGraphicsView
     QGraphicsPixmapItem *mainScreen;
     QPixmap              mainPixmap;
 
+    uint                 pixmapWidth;
+    uint                 contentXOffset;
     uint                 redraws;
 
     static SimScreen    *theScreen;
 
-  public:
+public:
     explicit SimScreen(QWidget *parent = 0);
     ~SimScreen();
 
-  public:
+public:
     void        setScale(qreal _scale);
     void        updatePixmap();
     void        refreshScreen();
     static void update_pixmap() { theScreen->updatePixmap(); }
     static void refresh_lcd()   { theScreen->refreshScreen(); }
     static uint redraw_count()  { return theScreen->redraws; }
+    void        setPixmapGeometry(int totalWidth, int xOffset);
 };
 
 #endif // WASM

sim/sim-window.cpp

@@ -273,29 +273,46 @@ void MainWindow::resizeEvent(QResizeEvent * event)
         kh = keyboard_height * kr;
     }
 
-    // Set screen ratio and geometry (full width, at top)
-    int x = 0;
-    int y = 0;
+    // Set screen ratio and geometry
+    int xOffset      = (nw - scaledSW) / 2;
+    int yOffset      = (nh - scaledSH - kh) / 2;
+    int screenWidth  = scaledSW;
+    int screenHeight = scaledSH;
+
 #ifdef ANDROID
+    // On Android: use a wider pixmap with black bars and position at x=0
+    // This is because the primary screen needs to be at x=0, otherwise
+    // we observe really weird refresh delays on the leftmost columns
     QScreen *screen = QGuiApplication::primaryScreen();
     if (screen)
     {
-        // Or get the available geometry (excludes system UI like status bar)
         QRect availableGeometry = screen->availableGeometry();
         int availableWidth = availableGeometry.width();
-        int availableHeight = availableGeometry.height();
-        x = (availableWidth - nw) / 2;
-        y = (availableHeight - nh) / 2;
+        xOffset = (availableWidth - nw) / 2;
+
+        // Calculate where LCD content should be drawn within the pixmap
+        int unscaledPixmapWidth = availableWidth / sr;
+        int unscaledContentX = (xOffset + (nw - scaledSW) / 2) / sr;
+
+        // Ensure pixmap is wide enough
+        int requiredPixmapWidth = unscaledContentX + ui.screen->screen_width;
+        if (unscaledPixmapWidth < requiredPixmapWidth)
+            unscaledPixmapWidth = requiredPixmapWidth;
+
+        // Set the pixmap to span the full width with black bars
+        ui.screen->setPixmapGeometry(unscaledPixmapWidth, unscaledContentX);
+        screenWidth = unscaledPixmapWidth * sr;
+        xOffset = 0;
+        nw = availableWidth;
     }
-#endif
+#endif // ANDROID
 
-    QRect sframe(x + (nw - scaledSW) / 2, y, scaledSW, scaledSH);
+    // Position the screen view (always at x=0 on Android)
+    QRect sframe(xOffset, yOffset, screenWidth, screenHeight);
     ui.screen->setGeometry(sframe);
     ui.screen->setScale(sr);
 
-    // Set keyboard size (centered horizontally, with spacing from screen)
-    qreal spacing = (nh - scaledSH - kh) / 2;
-    QRect kframe(x + (nw - kw) / 2, y + scaledSH + spacing, kw, kh);
+    QRect kframe((nw - kw) / 2, yOffset + screenHeight, kw, kh);
     ui.keyboard->setGeometry(kframe);
 }