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| -rw-r--r-- | ui/gtk.c | 65 |
1 files changed, 65 insertions, 0 deletions
diff --git a/ui/gtk.c b/ui/gtk.c index 982037b2c0..9f3171abc5 100644 --- a/ui/gtk.c +++ b/ui/gtk.c @@ -800,6 +800,71 @@ void gd_update_monitor_refresh_rate(VirtualConsole *vc, GtkWidget *widget) #endif } +/** + * DOC: Coordinate handling. + * + * We are coping with sizes and positions in various coordinates and the + * handling of these coordinates is somewhat confusing. It would benefit us + * all if we define these coordinates explicitly and clearly. Besides, it's + * also helpful to follow the same naming convention for variables + * representing values in different coordinates. + * + * I. Definitions + * + * - (guest) buffer coordinate: this is the coordinates that the guest will + * see. The x/y offsets and width/height specified in commands sent by + * guest is basically in buffer coordinate. + * + * - (host) pixel coordinate: this is the coordinate in pixel level on the + * host destop. A window/widget of width 300 in pixel coordinate means it + * occupies 300 pixels horizontally. + * + * - (host) logical window coordinate: the existence of global scaling + * factor in desktop level makes this kind of coordinate play a role. It + * always holds that (logical window size) * (global scale factor) = + * (pixel size). + * + * - global scale factor: this is specified in desktop level and is + * typically invariant during the life cycle of the process. Users with + * high-DPI monitors might set this scale, for example, to 2, in order to + * make the UI look larger. + * + * - zooming scale: this can be freely controlled by the QEMU user to zoom + * in/out the guest content. + * + * II. Representation + * + * We'd like to use consistent representation for variables in different + * coordinates: + * - buffer coordinate: prefix fb + * - pixel coordinate: prefix p + * - logical window coordinate: prefix w + * + * For scales: + * - global scale factor: prefix gs + * - zooming scale: prefix scale/s + * + * Example: fbw, pw, ww for width in different coordinates + * + * III. Equation + * + * - fbw * gs * scale_x = pw + * - pw = gs * ww + * + * Consequently we have + * + * - fbw * scale_x = ww + * + * Example: assuming we are running QEMU on a 3840x2160 screen and have set + * global scaling factor to 2, if the guest buffer size is 1920x1080 and the + * zooming scale is 0.5, then we have: + * - fbw = 1920, fbh = 1080 + * - pw = 1920, ph = 1080 + * - ww = 960, wh = 540 + * A bonus of this configuration is that we can achieve pixel to pixel + * presentation of the guest content. + */ + static gboolean gd_draw_event(GtkWidget *widget, cairo_t *cr, void *opaque) { VirtualConsole *vc = opaque; |