Fix rendering artifacts

Fix artifacts that occur when Qt is requested to render SVGs into very small pixmaps. This is done by making sure that the SVG is always rendered into pixmaps that are at least 24x24 in size (the size of the original PNG pixmap).

Adjust the pixmap drawing code so that a potentially larger source pixmap is drawn into a smaller target pixmap.

src/gui/clips/MidiClipView.cpp

@@ -441,11 +441,15 @@ void MidiClipView::paintEvent( QPaintEvent * )
 
 		// scale step graphics to fit the beat clip length
 		int const stepWidth = w / steps;
+		// Make sure that the pixmaps will be at least 24 pixels wide.
+		// There are artifacts if SVGs are rendered into very small pixmaps.
+		int const sourcePixmapWidth = std::max(stepWidth, 24);
 		int const stepHeight = std::max(24, rect().height() - 2 * BeatStepButtonOffset);
-		QPixmap const stepon0 = embed::getIconPixmap("step_btn_on_0", stepWidth, stepHeight);
-		QPixmap const stepon200 = embed::getIconPixmap("step_btn_on_200", stepWidth, stepHeight);
-		QPixmap const stepoff = embed::getIconPixmap("step_btn_off", stepWidth, stepHeight);
-		QPixmap const stepoffl = embed::getIconPixmap("step_btn_off_light", stepWidth, stepHeight);
+
+		QPixmap const stepon0 = embed::getIconPixmap("step_btn_on_0", sourcePixmapWidth, stepHeight);
+		QPixmap const stepon200 = embed::getIconPixmap("step_btn_on_200", sourcePixmapWidth, stepHeight);
+		QPixmap const stepoff = embed::getIconPixmap("step_btn_off", sourcePixmapWidth, stepHeight);
+		QPixmap const stepoffl = embed::getIconPixmap("step_btn_off_light", sourcePixmapWidth, stepHeight);
 
 		for (int it = 0; it < steps; it++)	// go through all the steps in the beat clip
 		{
@@ -455,22 +459,25 @@ void MidiClipView::paintEvent( QPaintEvent * )
 			const int x = BORDER_WIDTH + static_cast<int>(it * w / steps);
 			const int y = BeatStepButtonOffset;
 
+			QRect target(x, y, stepWidth, stepHeight);
+			QRect source(0, 0, sourcePixmapWidth, stepHeight);
+
 			if (n)
-			{
+			{	
 				const int vol = n->getVolume();
-				p.drawPixmap(x, y, stepoffl);
-				p.drawPixmap(x, y, stepon0);
+				p.drawPixmap(target, stepoffl, source);
+				p.drawPixmap(target, stepon0, source);
 				p.setOpacity(std::sqrt(vol / 200.0));
-				p.drawPixmap(x, y, stepon200);
+				p.drawPixmap(target, stepon200, source);
 				p.setOpacity(1);
 			}
 			else if ((it / 4) % 2)
 			{
-				p.drawPixmap(x, y, stepoffl);
+				p.drawPixmap(target, stepoffl, source);
 			}
 			else
 			{
-				p.drawPixmap(x, y, stepoff);
+				p.drawPixmap(target, stepoff, source);
 			}
 		} // end for loop