Simply the matrix calculation for zooming
In order to apply the zoom transformation to the output matrix, Weston was
doing the following:
• Create a temporary matrix to hold the translation
• Invert the translation matrix using weston_matrix_invert into
another temporary matrix
• Scale that matrix by the scale factor
• Multiply the current matrix with the temporary matrix
Using weston_matrix_invert to invert a translation matrix is over the top.
Instead we can just negate the values we pass to weston_matrix_translate.
Matrix multiplication is associative so creating a temporary matrix to hold the
scale and translation transform should be equivalent to just applying them
directly to the output matrix.
diff --git a/src/compositor.c b/src/compositor.c
index a35c578..ee8dc24 100644
--- a/src/compositor.c
+++ b/src/compositor.c
@@ -3188,8 +3188,6 @@
weston_output_update_matrix(struct weston_output *output)
{
float magnification;
- struct weston_matrix camera;
- struct weston_matrix modelview;
weston_matrix_init(&output->matrix);
weston_matrix_translate(&output->matrix,
@@ -3204,14 +3202,11 @@
if (output->zoom.active) {
magnification = 1 / (1 - output->zoom.spring_z.current);
- weston_matrix_init(&camera);
- weston_matrix_init(&modelview);
weston_output_update_zoom(output);
- weston_matrix_translate(&camera, output->zoom.trans_x,
- -output->zoom.trans_y, 0);
- weston_matrix_invert(&modelview, &camera);
- weston_matrix_scale(&modelview, magnification, magnification, 1.0);
- weston_matrix_multiply(&output->matrix, &modelview);
+ weston_matrix_translate(&output->matrix, -output->zoom.trans_x,
+ output->zoom.trans_y, 0);
+ weston_matrix_scale(&output->matrix, magnification,
+ magnification, 1.0);
}
output->dirty = 0;