+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).
+}
+