Input images
This program uses two input images. An image file named background.jpg is used to create a background in the game window. Figure 1 shows what that image looks like when viewed in the Windows Paint program.
| Figure 1 . Background image in Windows Paint. |
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The ladybug image
The second input image is a file named ladybug.png , which is a picture of a red and black ladybug on a transparent black background. Figure 2 shows this image when viewed in the Windows Paint program.
| Figure 2 . Ladybug image in Windows Paint. |
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Figure 3 shows the same ladybug image when viewed in the Windows Picture and Fax Viewer program. Note that the black background from Figure 2 is transparent in Figure 3 .
| Figure 3 . Ladybug image in Windows Picture and Fax Viewer. |
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Figure 4 shows the same ladybug image when viewed in the Gimp image editor program. This program provides even a different treatment for the transparent pixels.
| Figure 4 . Ladybug image in Gimp. |
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The output image
Figure 5 shows a screen shot of the game window while the program is running
| Figure 5 . Output from program Slick0140a. |
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Different drawing parameters
The same ladybug image is drawn three times in Figure 5 with different drawing parameters.
The leftmost image of the ladybug in Figure 5 is drawn with a scale factor of 0.75 and a drawing mode that honors transparency:MODE_NORMAL.
The center image of the ladybug in Figure 5 is drawn using a different approach with a scale factor of 1.0 and a drawing mode thathonors transparency: MODE_NORMAL.
The rightmost image of the ladybug in Figure 4 is drawn using the same approach as the leftmost image, a scale factor of 1.25, anda drawing mode that does not honor transparency: MODE_ALPHA_BLEND.
Are the mode names reversed?
As mentioned above, the two images of the ladybug with transparency were drawn using a Slick2D constant named MODE_NORMAL .
The image of the ladybug on the right without transparency was drawn using a Slick2D constant named MODE_ALPHA_BLEND .
These names seem to have been reversed. I would expect the constant with a name that includes the words alpha and blend to honor transparency but that doesn't seem to be the case.
Beginning of the class named Slick0140a
Listing 1 shows the beginning of the class named Slick0140a including some instance variable declarations and the constructor.
| Listing 1 . Beginning of the class named Slick0140a. |
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public class Slick0140a extends BasicGame{
Image ladybug = null;Image background = null;
float leftX = 100;//leftmost position of ladybugfloat leftY = 100;float middleX = 200;//middle position of ladybug
float middleY = 50;float rightX = 300;//rightmost position of ladybugfloat rightY = 100;float leftScale = 0.75f;//drawing scale factorsfloat rightScale = 1.25f;
//----------------------------------------------------//public Slick0140a(){//constructor
//Set the titlesuper("Slick0140a, baldwin");
}//end constructor |
The instance variables shown in Listing 1 and the values that they contain will be used later to display the three ladybugimages shown in Figure 5 .