clear-grid-section

Arguments: grid-widget row-section column-section drawing-pane section-box

clear-grid-section is called internally whenever all or part of a grid-section (of a grid-widget) is redisplayed. For efficiency, it is called a single time to draw the empty background of an entire section before draw-cell is called for each of the individual visible cells of the section. The default method simply calls erase-contents-box to clear the section.

An application should not call this function, but may add methods to override the default method if desired. One case where this may be useful is to reduce flashing that may occur for example if clicking and dragging in a cell produces an animation effect by repeatedly changing the domain value represented by the cell and invalidating the cell to redraw it at each stage. If the draw-cell methods for all of the cells in the grid-section are written to draw the entire contents of the cells, then clear-grid-section need not do anything and so a method that does nothing could be added to eliminate the flashing caused by the default method clearing the background.

The arguments are:

• grid-widget: the grid-widget of which the grid-section is a part.
• row-section and column-section: these define the intersection where the clearing is done.
• drawing-pane: this is the child window on which drawing occurs. When clear-grid-section is called, the background-color of the drawing-stream is set to the background-color of the grid-widget.
• section-box: this is the box in the drawing-pane's stream coordinates that covers the section that should be cleared.

See also draw-cell, draw-grid-section, draw-grid and grid-widget.

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This page was not revised from the 8.1 page.
Created 2010.1.21.