hit_testing.pdf - Graphics Hit-testing Shape Models...

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Graphics Hit-testing Shape Models Selecting Lines and Shapes 2.7 Graphics Hit-testing 1
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Recap - Shape Model 2.7 Graphics Hit-testing 3 § an array of points: {P 1 , P 2 , … , P n } § isClosed flag (shape is polyline or polygon) § isFilled flag (polygon is filled or not) § (and stroke thickness, colours, etc.)
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Implementing Direct Manipulation 2.7 Graphics Hit-testing 4 § In a graphical interface, users expect to be able to select content using a mouse, and interact with it directly. - Includes graphical content, widgets etc. § Objective: test when a rendered shape is “selected” - Could be a filled or outlined polygon or a polyline - Selections that “just miss” the shape should “snap” to shape § How do you implement this? - Create a model of the shape - Draw it - Choose a “selection” paradigm - Implement shape hit tests - Respond to events
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Selection Paradigms 2.7 Graphics Hit-testing 5 § Hit-test selection - open shapes like lines and polyline use edge hit-test - closed shapes like rectangles, and polygons use inside hit-test § Alternate approaches we won’t cover: - Rubberband rectangle - Lasso
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Linear Algebra: Affine Space 2.7 Graphics Hit-testing 6 s a scalar : a single value (real number) v a vector : directed line segment (direction and magnitude) P a point :
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Christopher Reinemann
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