Manually position and scale the content

Position and scale the content "manually" instead of relying on the
renderer "logical size".

This avoids possible rounding differences between the computed window
size and the content size, causing one row or column of black pixels on
the bottom or on the right.

This also avoids HiDPI scale issues, by computing the scaling manually.

This will also enable to draw items at their expected size on the screen
(unscaled).

Fixes #15 <https://github.com/Genymobile/scrcpy/issues/15>

app/src/screen.h

@@ -29,6 +29,8 @@ struct screen {
 
     // client rotation: 0, 1, 2 or 3 (x90 degrees counterclockwise)
     unsigned rotation;
+    // rectangle of the content (excluding black borders)
+    struct SDL_Rect rect;
     bool has_frame;
     bool fullscreen;
     bool maximized;
@@ -56,6 +58,12 @@ struct screen {
         .height = 0, \
     }, \
     .rotation = 0, \
+    .rect = { \
+        .x = 0, \
+        .y = 0, \
+        .w = 0, \
+        .h = 0, \
+    }, \
     .has_frame = false, \
     .fullscreen = false, \
     .maximized = false, \
@@ -89,8 +97,11 @@ bool
 screen_update_frame(struct screen *screen, struct video_buffer *vb);
 
 // render the texture to the renderer
+//
+// Set the update_content_rect flag if the window or content size may have
+// changed, so that the content rectangle is recomputed
 void
-screen_render(struct screen *screen);
+screen_render(struct screen *screen, bool update_content_rect);
 
 // switch the fullscreen mode
 void
@@ -117,4 +128,11 @@ screen_handle_window_event(struct screen *screen, const SDL_WindowEvent *event);
 struct point
 screen_convert_to_frame_coords(struct screen *screen, int32_t x, int32_t y);
 
+// Convert coordinates from window to drawable.
+// Events are expressed in window coordinates, but content is expressed in
+// drawable coordinates. They are the same if HiDPI scaling is 1, but differ
+// otherwise.
+void
+screen_hidpi_scale_coords(struct screen *screen, int32_t *x, int32_t *y);
+
 #endif