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An object of this class is used to paint a Grayscale plot of a 3D surface ranging from black at the lowest elevation to white at the highestelevation. The various shades of gray vary in a smooth gradient between the two extremes. The leftmost image in Figure 1 is an example of the type of plot produced by an object of this class.
| Listing 14. Beginning of the class named CanvasType0surface. |
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class CanvasType0surface extends Canvas{
CanvasType0surface(){//constructorsetSize(dataWidth * blockSize,
dataHeight * blockSize);getCenter();
}//end constructor |
The constructor for the class is straightforward. It accesses instance variables of the outer enclosing object to set the size of the canvas on thebasis of the size of the surface and the size of the square of pixels that will be used to represent each elevation value on the surface.
The constructor also calls the getCenter method to get the coordinates of the center of the surface in order to be able to draw theoptional red axes in the correct position later.
The real work is done by the overridden paint method, which begins in Listing 15 . Of the three classes used to plot the 3D surface, this is the simplest.
| Listing 15. Beginning of overridden paint method. |
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public void paint(Graphics g){
Color color = null;for(int row = 0;row<dataHeight;row++){
for(int col = 0;col<dataWidth;col++){
//Add in red, green, and blue in// proportion to the value of the
// surface height.int red = (int)data[row][col];
int green = red;int blue = red; |
The purpose of this overridden paint method is to convert the elevation value of each point on the 3D surface into an appropriate shade ofgray, and to paint a square of pixels on the screen at that elevation value's location where every pixel in the square is the same shade of gray.
In order to produce a gray pixel in a 24-bit color system, you need to set the color values for red, green, and blue to the same value. If all three colorvalues are zero, the pixel color is black. If all three color values are 255, the pixel color is white. If all three color values fall somewhere in betweenzero and 255, the pixel color will be some shade of gray.
Recall that the elevation values were earlier normalized to fall in the range from zero to 255. The code in Listing 15 uses a nested for loop to access every elevation value in the array that describes the 3D surface. Thenit sets the red, green, and blue color values to the normalized surface valuefor each point on the 3D surface.
Continuing inside the nested for loops, the code in Listing 16 instantiates a new object of type Color based on the current red, green, and blue color values.
| Listing 16. Instantiate a Color object. |
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color = new Color(red,green,blue); |
The code in Listing 17 calls the setColor method of the Graphics class to set the current drawing color to the color described by the Color object referred to by the reference variable named color .
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