To display dialogs atop the game graphics, backends must provide an overlay mode.
The overlay is currently forced at 16 bpp.
For 'coolness' we usually want to have an overlay that is blended over the game graphics. On backends that support alpha blending, this is no issue but on other systems this needs some trickery.
Essentially, we fake (alpha) blending on these systems by copying the current game graphics into the overlay buffer when activating the overlay, and then manually compose whatever graphics we want to show in the overlay. This works because we assume the game to be "paused" whenever an overlay is active.
◆ showOverlay()
| virtual void OSystem::showOverlay |
( |
| ) |
|
|
pure virtual |
Activate the overlay mode.
◆ hideOverlay()
| virtual void OSystem::hideOverlay |
( |
| ) |
|
|
pure virtual |
Deactivate the overlay mode.
◆ isOverlayVisible()
| virtual bool OSystem::isOverlayVisible |
( |
| ) |
const |
|
pure virtual |
Return true if the overlay mode is activated, false otherwise.
◆ getOverlayFormat()
| virtual Graphics::PixelFormat OSystem::getOverlayFormat |
( |
| ) |
const |
|
pure virtual |
Return the pixel format description of the overlay.
- See also
- Graphics::PixelFormat
◆ clearOverlay()
| virtual void OSystem::clearOverlay |
( |
| ) |
|
|
pure virtual |
Reset the overlay.
After calling this method while the overlay mode is active, the user should be seeing only the game graphics. How this is achieved depends on how the backend implements the overlay. It either sets all pixels of the overlay to be transparent (when alpha blending is used) or, in case of fake alpha blending, it might just put a copy of the current game graphics screen into the overlay.
◆ grabOverlay()
| virtual void OSystem::grabOverlay |
( |
void * |
buf, |
|
|
int |
pitch |
|
) |
| |
|
pure virtual |
Copy the content of the overlay into a buffer provided by the caller.
This is only used to implement fake alpha blending.
◆ copyRectToOverlay()
| virtual void OSystem::copyRectToOverlay |
( |
const void * |
buf, |
|
|
int |
pitch, |
|
|
int |
x, |
|
|
int |
y, |
|
|
int |
w, |
|
|
int |
h |
|
) |
| |
|
pure virtual |
Blit a graphics buffer to the overlay.
In a sense, this is the reverse of grabOverlay.
- Parameters
-
| buf | Buffer containing the graphics data source. |
| pitch | Pitch of the buffer (number of bytes in a scanline). |
| x | x coordinate of the destination rectangle. |
| y | y coordinate of the destination rectangle. |
| w | Width of the destination rectangle. |
| h | Height of the destination rectangle. |
- See also
- copyRectToScreen
-
grabOverlay
◆ getOverlayHeight()
| virtual int16 OSystem::getOverlayHeight |
( |
| ) |
|
|
pure virtual |
Return the height of the overlay.
- See also
- getHeight
◆ getOverlayWidth()
| virtual int16 OSystem::getOverlayWidth |
( |
| ) |
|
|
pure virtual |
Return the width of the overlay.
- See also
- getWidth
1.8.13