Advanced Java Screen Update Techniques SD

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Advanced Java Screen Update TechniquesSD98 -
Session 4406

• Ted Faison
• ted.faison_at_computer.org
• Faison Computing Inc.
• www.faisoncomputing.com

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Painting with the 2D API

• Everything is just a Shape
• The Shape interface and its main methods
• boolean contains(Point2D)
• Rectangle getBounds()
• PathIterator getPathIterator(AffineTransform)
• boolean Intersects(Rectangle2D)
• GeneralPath, Bezier Curves
• Rectangles, Polygons, Ellipses, Arcs
• Text

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2D Drawing Examples

• Drawing a geometric shape
• DrawingRectangles.java
• Filling a shape
• FillingRectangles.java
• Drawing the outline of a shape
• TextOutline.java

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Flicker and repaint ( )

• What repaint() does
• Erases component background
• Sets graphics context color
• Calls paint()
• Flicker is produced by the background erasure
• Example
• RectWithFlicker.java

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Minimizing Flicker

• Tips
• Call paint() directly, instead of repaint(), if
  the component has no transparent areas
• Don't erase areas you're going to paint over

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Moving components on the screen

• SetLocation causes the AWT to erase the old image
  and draw the new one.
• Can cause flicker, since no optimizations are
  applied
• Use a silhouette
• a lightweight outline XORed to the screen
• Extremely fast
• Example UsingSilhouettes.java

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Double Buffering

• An example
• OffScreenImage.java
• Using BufferedImage
• gives control over transparency and blending
• examples
• OffScreenBufferedImage.java
• OffScreenBufferedImageWithTransparency.java

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Shaping the area painted Clipping Regions

• Using Graphics.setClip
• JDK 1.1 supported only rect
• Graphics.setClip(int, int, int, int)
• JDK 1.2 also supports arbitrary shapes
• Graphics2D.setClip(Shape)

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Improving Screen Update Speed with Clipping

• Use rectangular clipping areas only
• Examples
• Rectangles RectMovingWithClipping.java
• Images ImageMovingWithClipping .java
• Shapes ShapeMovingWithClipping.java
• uses coordinate transformations to move shape

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Coordinate Transformations

• Functions that map a point in one space to a
  point in another space
• Represented using a 3x3 matrix
• Transformations require multiplying each pixel by
  the transformation matrix
• Positive angles rotate the X axis towards the Y
  axis
• Can be used to invert axes, bend images, distort
  space arbitrarily

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Coordinate Transformations
a11 a12 a13 a21 a22 a23 0 0 1
x y 1
a11x a12y a13 a21x a22y a23 0 0
1
x y 1


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Affine Transforms

• Maintain straightness and parallelism
• Translation
• setToTranslation(double dx, double, dy)
• used to support graphics scrolling

Device Space
User Space
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Affine Transforms

• Rotation
• Rotating about the origin
• setToRotation(double theta)

Device Space
User Space
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Affine Transforms

• Rotation about an arbitrary point
• SetToRotation(theta, x, y)

(x, y)
(x, y)
Device Space
User Space
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Affine Transforms

• Shearing
• setToShear(double sh, double sy)

Device Space
User Space
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Affine Transforms

• Scaling
• setToScale(double sx, double sy)
• anisotropic vs isotropic scaling

Device Space
User Space
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Affine Transforms

• Handling transformed images with offscreen
  buffers
• Examples
• OffScreenTransformedImage.java
• ScalingImages.java
• RotatingImages.java
• ShearingImages.java

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Batch Painting

• A technique to speed up rendering
• Used internally by the Graphics2D context
• Batch a block of contiguous pixels with the same
  Paint object

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Drawing Patterns

• Patterns require BufferedImage and TexturePaint
  objects
• Example PatternedBackgrounds.java
• Filling Shapes with Patterns
• Example FillingShapeWithPattern.java
• Example FillingTextWithPattern.java

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Conclusion

• Use Double Buffering to minimize flicker
• Use Coordinate Transformations to scroll and zoom
  
• Everything is a Shape, with support for stroking,
  gradient filling and pattern filling
• Batch painting internally increases screen update
  speed