Android for Game Developers - Beginning Android Games - page 171

Drawing Lines
To draw a line, we can use the following Canvas method:
Canvas.drawLine(float startX, float startY, float stopX, float stopY, Paint paint);
The first two arguments specify the coordinates of the starting point of the line, the next two
arguments specify the coordinates of the endpoint of the line, and the last argument specifies a
Paint instance. The line that gets drawn will be one pixel thick. If we want the line to be thicker,
we can specify its thickness in pixels by setting the stroke width of the Paint instance:
Paint.setStrokeWidth(float widthInPixels);
Drawing Rectangles
We can also draw rectangles with the following Canvas method:
Canvas.drawRect(float topleftX, float topleftY, float bottomRightX, float bottomRightY,
Paint paint);
The first two arguments specify the coordinates of the top-left corner of the rectangle, the next
two arguments specify the coordinates of the bottom-left corner of the rectangle, and the Paint
specifies the color and style of the rectangle. So what style can we have and how do we set it?
To set the style of a Paint instance, we call the following method:
Paint.setStyle(Style style);
Style is an enumeration that has the values Style.FILL , Style.STROKE , and Style.FILL_AND_
STROKE . If we specify Style.FILL , the rectangle will be filled with the color of the Paint . If we
specify Style.STROKE , only the outline of the rectangle will be drawn, again with the color and
stroke width of the Paint . If Style.FILL_AND_STROKE is set, the rectangle will be filled, and the
outline will be drawn with the given color and stroke width.
Drawing Circles
More fun can be had by drawing circles, either filled or stroked (or both):
Canvas.drawCircle(float centerX, float centerY, float radius, Paint paint);
The first two arguments specify the coordinates of the center of the circle, the next argument
specifies the radius in pixels, and the last argument is again a Paint instance. As with the
Canvas.drawRectangle() method, the color and style of the Paint will be used to draw the circle.
Blending
One last thing of importance is that all of these drawing methods will perform alpha blending.
Just specify the alpha of the color as something other than 255 (0xff), and your pixels, lines,
rectangles, and circles will be translucent.