added software renderer. split common functions prev.

in gleswidget to renderstack (a QStackWidget), which in
turn calls an actual renderer. added ability to target GLES
directly, but this is maybe uneeded.

src/qt/qt_rendererstack.hpp

@@ -0,0 +1,60 @@
+#ifndef QT_RENDERERCONTAINER_HPP
+#define QT_RENDERERCONTAINER_HPP
+
+#include <QStackedWidget>
+#include <QKeyEvent>
+
+namespace Ui {
+class RendererStack;
+}
+
+class RendererStack : public QStackedWidget
+{
+    Q_OBJECT
+
+public:
+    explicit RendererStack(QWidget *parent = nullptr);
+    ~RendererStack();
+
+    void mousePressEvent(QMouseEvent* event) override;
+    void mouseReleaseEvent(QMouseEvent* event) override;
+    void mouseMoveEvent(QMouseEvent* event) override;
+    void wheelEvent(QWheelEvent *event) override;
+    void keyPressEvent(QKeyEvent* event) override
+    {
+        event->ignore();
+    }
+    void keyReleaseEvent(QKeyEvent* event) override
+    {
+        event->ignore();
+    }
+
+signals:
+    void blitToRenderer(const QImage& img, int, int, int, int);
+
+public slots:
+    void blit(int x, int y, int w, int h);
+    void mousePoll();
+
+private slots:
+    void on_RendererStack_currentChanged(int arg1);
+
+private:
+    Ui::RendererStack *ui;
+
+    struct mouseinputdata {
+        int deltax, deltay, deltaz;
+        int mousebuttons;
+    };
+    mouseinputdata mousedata;
+
+    int x, y, w, h, sx, sy, sw, sh;
+
+    // always have a qimage available for writing, which is _probably_ unused
+    // worst case - it will just get reallocated because it's refcounter is > 1
+    // when calling bits();
+    int currentBuf = 0;
+    QVector<QImage> imagebufs;
+};
+
+#endif // QT_RENDERERCONTAINER_HPP