Draw Context Data Structure

QuickDraw 3D defines the draw context data structure to maintain information that is common to all the supported draw contexts. The draw context data structure is defined by the TQ3DrawContextData data type.

typedef struct TQ3DrawContextData {
    TQ3DrawContextClearImageMethod                  clearImageMethod;
    TQ3ColorARGB                                    clearImageColor;
    TQ3Area                                         pane;
    TQ3Boolean                                      paneState;
    TQ3Bitmap                                       mask;
    TQ3Boolean                                      maskState;
    TQ3Boolean                                      doubleBufferState;
} TQ3DrawContextData;


clearImageMethod

A constant that indicates how the drawing destination should be cleared. You can use these constants to specify a method to clear the image.

                    typedef enum TQ3DrawContextClearImageMethod {
                        kQ3ClearMethodNone,
                        kQ3ClearMethodWithColor,
                    } TQ3DrawContextClearImageMethod;


The constant kQ3ClearMethodNone indicates that the drawing destination should not be cleared. The exact behavior when Q3View_StartRendering is called is renderer-dependent. For example, some renderers expect to redraw every pixel in the drawing destination. By specifying kQ3ClearMethodNone , you allow those renderers to apply optimizations during rendering. The constant kQ3ClearMethodWithColor indicates that the drawing destination should be cleared with the color specified in the clearImageColor field.

clearImageColor

The color to be used when clearing the drawing destination with a color. This field is ignored unless the value in the clearImageMethod field is kQ3ClearMethodWithColor .

pane

The rectangular area (specified in window coordinates) in the drawing destination within which all drawing occurs. If the output pane is smaller than the window's port rectangle, the image is scaled (not clipped) to fit into the pane.

paneState

A Boolean value that determines whether the area specified in the pane field is to be used ( kQ3True ) or is to be ignored ( kQ3False ). Set this field to kQ3False to use the entire window as the output pane. If this field is set to kQ3True , the pane field must contain a valid area.

mask

A bitmap that is used to mask out certain portions of the drawing destination. Each bit in the bitmap corresponds to a pixel in the drawing area. If a bit is set, the corresponding pixel is drawn; if a bit is clear, the corresponding pixel is not drawn. If the value in this field is NULL , the entire window is used as the clipping region.

maskState

A Boolean value that determines whether the mask specified in the mask field is to be used ( kQ3True ) or is to be ignored ( kQ3False ). If this field is set to kQ3True , the mask field must contain a valid bitmap.

doubleBufferState

A Boolean value that determines whether double buffering is to used for the drawing destination ( kQ3True ) or not ( kQ3False ). When double buffering is enabled, the back buffer is the active buffer.

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© 1997 Apple Computer, Inc.

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