viewer: implemented basic zoom

No scrolling functionality yet, but the zoom is functional and efficient.

app/widget/viewer/viewersizer.cpp

@@ -1,9 +1,12 @@
 #include "viewersizer.h"
 
+#include <QMatrix4x4>
+
 ViewerSizer::ViewerSizer(QWidget *parent) :
   QWidget(parent),
   widget_(nullptr),
-  aspect_ratio_(0)
+  aspect_ratio_(0),
+  zoom_(0)
 {
 }
 
@@ -23,15 +26,25 @@ void ViewerSizer::SetWidget(QWidget *widget)
 
 void ViewerSizer::SetChildSize(int width, int height)
 {
-  if (height == 0) {
+  width_ = width;
+  height_ = height;
+
+  if (!width_ || !height_) {
     aspect_ratio_ = 0;
   } else {
-    aspect_ratio_ = static_cast<double>(width) / static_cast<double>(height);
+    aspect_ratio_ = static_cast<double>(width_) / static_cast<double>(height_);
   }
 
   UpdateSize();
 }
 
+void ViewerSizer::SetZoom(int percent)
+{
+  zoom_ = percent;
+
+  UpdateSize();
+}
+
 void ViewerSizer::resizeEvent(QResizeEvent *event)
 {
   QWidget::resizeEvent(event);
@@ -53,21 +66,51 @@ void ViewerSizer::UpdateSize()
 
   widget_->setVisible(true);
 
-  double our_aspect_ratio = static_cast<double>(width()) / static_cast<double>(height());
+  QSize child_size;
+  QMatrix4x4 child_matrix;
 
-  QPoint child_pos;
-  QSize child_size = size();
+  if (zoom_ <= 0) {
+
+    // If zoom is 0, we auto-fit
+    double our_aspect_ratio = static_cast<double>(width()) / static_cast<double>(height());
+
+    child_size = size();
+
+    if (our_aspect_ratio > aspect_ratio_) {
+      // This container is wider than the image, scale by height
+      child_size = QSize(qRound(child_size.height() * aspect_ratio_), height());
+    } else {
+      // This container is taller than the image, scale by width
+      child_size = QSize(width(), qRound(child_size.width() / aspect_ratio_));
+    }
 
-  if (our_aspect_ratio > aspect_ratio_) {
-    // This container is wider than the image, scale by height
-    child_size.setWidth(qRound(child_size.height() * aspect_ratio_));
-    child_pos.setX(width() / 2 - child_size.width() / 2);
   } else {
-    // This container is taller than the image, scale by width
-    child_size.setHeight(qRound(child_size.width() / aspect_ratio_));
-    child_pos.setY(height() / 2 - child_size.height() / 2);
+
+    float x_scale = 1.0f;
+    float y_scale = 1.0f;
+
+    int zoomed_width = qRound(width_ * static_cast<double>(zoom_) * 0.01);
+    int zoomed_height = qRound(height_ * static_cast<double>(zoom_) * 0.01);
+
+    if (zoomed_width > width()) {
+      x_scale = static_cast<double>(zoomed_width) / static_cast<double>(width());
+      zoomed_width = width();
+    }
+
+    if (zoomed_height > height()) {
+      y_scale = static_cast<double>(zoomed_height) / static_cast<double>(height());
+      zoomed_height = height();
+    }
+
+    // Rather than make a huge surface, we still crop at our width/height and then signal a matrix
+    child_matrix.scale(x_scale, y_scale, 1.0F);
+
+    child_size = QSize(zoomed_width, zoomed_height);
+
   }
 
   widget_->resize(child_size);
-  widget_->move(child_pos);
+  widget_->move(width() / 2 - child_size.width() / 2, height() / 2 - child_size.height() / 2);
+
+  emit RequestMatrix(child_matrix);
 }