Controlling Hardware Scaling3

QuickTime 1.6.1 added three functions that allow applications to zoom a monitor (GDHasScale , GDGetScale , and GDSetScale ). These three functions are considered low-level calls (comparable to SetEntries ) that you should use only when playing back QuickTime movies in a controlled environment with no user interaction. Also, because this capability is not present on all computers, applications should not depend on its availability.

These new functions provide a standard way for you to access the resizing abilities of a user's monitor for playback. Effectively, this allows you to have full screen Cinepak playback on low-end Macintosh computers.

GDHasScale

Returns the closest possible scaling that a particular screen device can be set to in a given pixel depth.



 
pascal OSErr GDHasScale (

                     GDHandle gdh,

                     short depth,

                     Fixed *scale);

gdh: Contains a handle to a screen graphics device.
depth: Specifies the pixel depth of the screen device.
scale: Points to a fixed point scale value. On input, this field should be set to the desired scale value. On output, this field will contain the closest scale available for the given depth. A scale of 0x10000 indicates normal size, 0x20000 indicates double size, and so on.

DISCUSSION

The GDHasScale function returns scaling information for a particular GDevice for a requested depth. This function allows you to query a GDevice without actually changing it. For example, if you specify 0x20000 but the GDevice does not support it, GDHasScale returns with noErr and a scale of 0x10000. Because this function checks for a supported depth, your requested depth must be supported by the GDevice. GDHasScale references the video driver through the graphics device structure.

RESULT CODES

`CDepthErr`	-157	The requested depth is not supported
`cDevErr`	-155	Not a screen device
`controlErr`	-17	Video driver cannot respond to this call

GDGetScale

Returns the current scale of the given screen graphics device.



 
pascal OSErr GDGetScale (

                     GDHandle gdh,

                     Fixed *scale,

                     short *flags);

gdh: Contains a handle to a screen graphics device.
scale: Points to a fixed point field to hold the scale result.
flags: Points to a short integer. It returns the status parameter flags for the video driver. For now, 0 is always returned in this field.

RESULT CODES

`cDevErr`	-155	Not a screen device
`controlErr`	-17	Video driver cannot respond to this call

GDSetScale

Sets a screen graphics device to a new scale.



 
pascal OSErr GDSetScale (

                     GDHandle gdh,

                     Fixed scale,

                     short flags);

gdh: Contains a handle to a screen graphics device.
scale: A fixed point scale value.
flags: Points to a short integer. It returns the status parameter flags for the video driver. For now, 0 is always returned in this field.

RESULT CODES

`cDevErr`	-155	Not a screen device
`controlErr`	-17	Video driver cannot respond to this call