Allow to automatically scale nanovg viewport, used in blendish

Signed-off-by: falkTX <falktx@falktx.com>

dgl/SubWidget.hpp

@@ -129,7 +129,7 @@ public:
    /**
       Indicate that this subwidget will always draw at its own internal size and needs scaling to fit target size.
     */
-    void setNeedsViewportScaling(bool needsViewportScaling = true);
+    void setNeedsViewportScaling(bool needsViewportScaling = true, double autoScaleFactor = 0.0);
 
    /**
       Indicate that this subwidget should not be drawn on screen, typically because it is managed by something else.

dgl/src/OpenGL.cpp

@@ -575,21 +575,33 @@ void SubWidget::PrivateData::display(const uint width, const uint height, const
 
     bool needsDisableScissor = false;
 
-    if (needsFullViewportForDrawing || (absolutePos.isZero() && self->getSize() == Size<uint>(width, height)))
+    if (needsViewportScaling)
     {
-        // full viewport size
-        glViewport(0,
-                   -static_cast<int>(height * autoScaleFactor - height + 0.5),
-                   static_cast<int>(width * autoScaleFactor + 0.5),
-                   static_cast<int>(height * autoScaleFactor + 0.5));
+        // limit viewport to widget bounds
+        const int x = absolutePos.getX();
+        const int w = static_cast<int>(self->getWidth());
+        const int h = static_cast<int>(self->getHeight());
+
+        if (viewportScaleFactor != 0.0)
+        {
+            glViewport(x,
+                       -static_cast<int>(height * viewportScaleFactor - height + absolutePos.getY() + 0.5),
+                       static_cast<int>(width * viewportScaleFactor + 0.5),
+                       static_cast<int>(height * viewportScaleFactor + 0.5));
+        }
+        else
+        {
+            const int y = static_cast<int>(height - self->getHeight()) - absolutePos.getY();
+            glViewport(x, y, w, h);
+        }
     }
-    else if (needsViewportScaling)
+    else if (needsFullViewportForDrawing || (absolutePos.isZero() && self->getSize() == Size<uint>(width, height)))
     {
-        // limit viewport to widget bounds
-        glViewport(absolutePos.getX(),
-                   static_cast<int>(height - self->getHeight()) - absolutePos.getY(),
-                   static_cast<int>(self->getWidth()),
-                   static_cast<int>(self->getHeight()));
+        // full viewport size
+        glViewport(0,
+                   -static_cast<int>(height - height + 0.5),
+                   static_cast<int>(width + 0.5),
+                   static_cast<int>(height + 0.5));
     }
     else
     {

dgl/src/SubWidget.cpp

@@ -123,9 +123,10 @@ void SubWidget::setNeedsFullViewportDrawing(const bool needsFullViewportForDrawi
     pData->needsFullViewportForDrawing = needsFullViewportForDrawing;
 }
 
-void SubWidget::setNeedsViewportScaling(const bool needsViewportScaling)
+void SubWidget::setNeedsViewportScaling(const bool needsViewportScaling, const double autoScaleFactor)
 {
     pData->needsViewportScaling = needsViewportScaling;
+    pData->viewportScaleFactor = autoScaleFactor;
 }
 
 void SubWidget::setSkipDrawing(const bool skipDrawing)

dgl/src/SubWidgetPrivateData.cpp

@@ -28,7 +28,8 @@ SubWidget::PrivateData::PrivateData(SubWidget* const s, Widget* const pw)
       absolutePos(),
       needsFullViewportForDrawing(false),
       needsViewportScaling(false),
-      skipDrawing(false)
+      skipDrawing(false),
+      viewportScaleFactor(0.0)
 {
     parentWidget->pData->subWidgets.push_back(self);
 }

dgl/src/SubWidgetPrivateData.hpp

@@ -30,7 +30,8 @@ struct SubWidget::PrivateData {
     Point<int> absolutePos;
     bool needsFullViewportForDrawing; // needed for widgets drawing out of bounds
     bool needsViewportScaling; // needed for NanoVG
-    bool skipDrawing;
+    bool skipDrawing; // for context reuse in NanoVG based guis
+    double viewportScaleFactor; // auto-scaling for NanoVG
 
     explicit PrivateData(SubWidget* const s, Widget* const pw);
     ~PrivateData();