Make it possible to zoom the VideoWidget.

[pkanalytics] / video_widget.cpp

diff --git a/video_widget.cpp b/video_widget.cpp
index ba8cf51075b50661e820ae93d80813ae950a69e9..b25b938161851e6ee9f05b55c0277bd1084a59ea 100644 (file)
--- a/video_widget.cpp
+++ b/video_widget.cpp
@@ -31,6 +31,7 @@ extern "C" {
 #include <unordered_set>
 
 #include <QOpenGLFunctions>
+#include <QWheelEvent>
 
 using namespace std;
 using namespace std::chrono;
@@ -425,21 +426,118 @@ void VideoWidget::paintGL()
 
        glBegin(GL_QUADS);
 
+       // (0,0)
        glVertexAttrib2f(1, tx1, ty1);
-       glVertex2f(0.0f, 0.0f);
+       glVertex2f(zoom_matrix[2 * 3 + 0], zoom_matrix[2 * 3 + 1]);
 
+       // (0,1)
        glVertexAttrib2f(1, tx1, ty2);
-       glVertex2f(0.0f, 1.0f);
+       glVertex2f(zoom_matrix[1 * 3 + 0] + zoom_matrix[2 * 3 + 0], zoom_matrix[1 * 3 + 1] + zoom_matrix[2 * 3 + 1]);
 
+       // (1,1)
        glVertexAttrib2f(1, tx2, ty2);
-       glVertex2f(1.0f, 1.0f);
+       glVertex2f(zoom_matrix[0 * 3 + 0] + zoom_matrix[1 * 3 + 0] + zoom_matrix[2 * 3 + 0],
+                  zoom_matrix[1 * 3 + 0] + zoom_matrix[1 * 3 + 1] + zoom_matrix[2 * 3 + 1]);
 
+       // (1,0)
        glVertexAttrib2f(1, tx2, ty1);
-       glVertex2f(1.0f, 0.0f);
+       glVertex2f(zoom_matrix[0 * 3 + 0] + zoom_matrix[2 * 3 + 0],
+                  zoom_matrix[1 * 3 + 0] + zoom_matrix[2 * 3 + 1]);
 
        glEnd();
 }
 
+void matmul3x3(const double a[9], const double b[9], double res[9])
+{
+       for (int i = 0; i < 3; ++i) {
+               for (int j = 0; j < 3; ++j) {
+                       double sum = 0.0;
+                       for (int k = 0; k < 3; ++k) {
+                               sum += a[i * 3 + k] * b[k * 3 + j];
+                       }
+                       res[i * 3 + j] = sum;
+               }
+       }
+}
+
+void VideoWidget::wheelEvent(QWheelEvent *event)
+{
+       int delta = event->angleDelta().y();
+       if (delta == 0) {
+               return;
+       }
+       double x = event->position().x() / width();
+       double y = 1.0 - event->position().y() / height();
+       double zoom = delta > 0 ? pow(1.01, delta) : pow(1/1.01, -delta);
+
+       const double inv_translation_matrix[9] = {
+               1.0, 0.0, 0.0,
+               0.0, 1.0, 0.0,
+               -x, -y, 1.0
+       };
+       const double scale_matrix[9] = {
+               zoom, 0.0, 0.0,
+               0.0, zoom, 0.0,
+               0.0, 0.0, 1.0
+       };
+       const double translation_matrix[9] = {
+               1.0, 0.0, 0.0,
+               0.0, 1.0, 0.0,
+               x, y, 1.0
+       };
+       double tmp1[9], tmp2[9];
+       matmul3x3(zoom_matrix, inv_translation_matrix, tmp1);
+       matmul3x3(tmp1, scale_matrix, tmp2);
+       matmul3x3(tmp2, translation_matrix, zoom_matrix);
+
+       fixup_zoom_matrix();
+}
+
+// Normalize the matrix so that we never get skew or similar,
+// and also never can zoom or pan too far out.
+void VideoWidget::fixup_zoom_matrix()
+{
+       // Correct for any numerical errors (we know the matrix must be orthogonal
+       // and have zero rotation).
+       zoom_matrix[4] = zoom_matrix[0];
+       zoom_matrix[1] = zoom_matrix[2] = zoom_matrix[3] = zoom_matrix[5] = 0.0;
+       zoom_matrix[8] = 1.0;
+
+       // We can't zoom further out than 1:1. (Perhaps it would be nice to
+       // reuse the last zoom-in point to do this, but the center will have to do
+       // for now.)
+       if (zoom_matrix[0] < 1.0) {
+               const double zoom = 1.0 / zoom_matrix[0];
+               const double inv_translation_matrix[9] = {
+                       1.0, 0.0, 0.0,
+                       0.0, 1.0, 0.0,
+                       -0.5, -0.5, 1.0
+               };
+               const double scale_matrix[9] = {
+                       zoom, 0.0, 0.0,
+                       0.0, zoom, 0.0,
+                       0.0, 0.0, 1.0
+               };
+               const double translation_matrix[9] = {
+                       1.0, 0.0, 0.0,
+                       0.0, 1.0, 0.0,
+                       0.5, 0.5, 1.0
+               };
+               double tmp1[9], tmp2[9];
+               matmul3x3(zoom_matrix, inv_translation_matrix, tmp1);
+               matmul3x3(tmp1, scale_matrix, tmp2);
+               matmul3x3(tmp2, translation_matrix, zoom_matrix);
+       }
+
+       // Looking at the points we'll draw with glVertex2f(), make sure none of them are
+       // inside the square (which would generally mean we've panned ourselves out-of-bounds).
+       // We simply adjust the translation, which is possible because we fixed scaling above.
+       zoom_matrix[6] = min(zoom_matrix[6], 0.0);  // Left side (x=0).
+       zoom_matrix[7] = min(zoom_matrix[7], 0.0);  // Bottom side (y=0).
+       zoom_matrix[6] = std::max(zoom_matrix[6], 1.0 - zoom_matrix[0]);  // Right side (x=1).
+       zoom_matrix[7] = std::max(zoom_matrix[7], 1.0 - zoom_matrix[4]);  // Top side (y=1).
+}
+
 void VideoWidget::open(const string &filename)
 {
        stop();