JavaFX Effects and Blending

This chapter is from the book

JavaFX Developer's Guide

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This chapter is from the book

This chapter is from the book 

JavaFX Developer's Guide

Learn More Buy

Lighting

The final effect that we are going to look at is called Lighting. As its name suggests, it allows you to specify how a node or a group should be lit. Three different types of lighting can be used, all of which are represented by classes in the javafx.scene.effect.light package. The Lighting class itself, like all the other effects, is in the javafx.scene.effect package.

To define the lighting for a node or group, you create an instance of the Lighting class and install it in the effect variable of that node or group. Using lighting will make your scenes look more three-dimensional than they otherwise would, as you'll see in the examples in this section. The variables of the Lighting class are listed in Table 20-18.

Table 20-18. Variables of the Lighting Class

The light variable determines the type of lighting required, which must be one of DistantLight (which is the default), PointLight, and SpotLight. The other variables set the characteristics of the surface that will be lit and will be explained in the rest of this section by reference to examples.

The surfaceScale Variable

To create a 3D effect when lighting a 2D surface, the opacity value of each pixel is used as a guide to how "high" that pixel should appear to be when lit. Transparent pixels appear to be the lowest, while fully opaque pixels appear to be raised up from the surface. This effect can be increased or decreased by using the surfaceScale variable. Values that are greater than 1 cause the effect to be increased, while values between 0 and 1 cause it to be decreased. The same effect can also be seen at the edges of shapes.

The following code, which comes from the file javafxeffects/SurfaceScale.fx, shines a distant light on a rectangle. The details of the lighting are not important right now, but you'll see that the surfaceScale variable is bound to a slider. If you run this example, you can see the effect of varying the surfaceScale variable over its full range:

Rectangle {
    x: 20
    y: 20
    width: 100
    height: 100
    fill: Color.YELLOW
    effect: Lighting {
        light: DistantLight {
            azimuth: 0
            elevation: 30
        }
        surfaceScale: bind (scaleSlider.value as Number) / 10
    }
}

You can see how the surfaceScale value is used by comparing the two screenshots shown in Figure 20-32.

Figure 20-32 The surfaceScale variable of the Lighting effect

On the left of the figure, the surfaceScale value is 0, so there is no 3D effect at all. On the right, surfaceScale has its maximum possible value, and now you can see that the center of the rectangle appears to be raised up above its edges. The higher the surfaceScale value, the higher the center will appear to be.

The Bump Map

You can add additional surface relief by creating a bump map and installing it in the bumpInput variable of the Lighting effect. If this variable is null, the node on which the effect is applied is itself used to generate a bump map, which is what causes the 3D effect at the edges that you saw in Figure 20-32.

The bump map is just an Effect, which supplies pixels from which the relief of the lit surface is calculated. As before, the apparent height of a pixel on the lit shape depends on the opacity of the corresponding pixel of the bump map. This effect is affected by the value of the surfaceScale variable, as described in the preceding section.

A common way to specify a bump map is to create an image, set the opacity to reflect the contours that you want to appear in the finished result, and then turn it into an effect by using the Identity class that we discussed earlier in this chapter. The code in the file javafxeffects/BumpMap.fx shows how to apply a bump map in the form of an image file:

1      var logo = Image { url: "{__DIR__}javafxlogo.gif" };
2      Stage {
3          title: "Bump Map"
4          scene: Scene {
5              width: 240
6              height: 140
7              fill: Color.BLACK
8              content: [
9                  Rectangle {
10                     x: 20
11                     y: 20
12                     width: 200
13                     height: 100
14                     fill: Color.YELLOW
15                     effect: Lighting {
16                         light: DistantLight {
17                             azimuth: 90
18                             elevation: 25
19                         }
20                         bumpInput: Identity {
21                             source: logo
22                             x: 30
23                             y: 40
24                         }
25                     }
26                 }
27             ]
28         }
29     }

The code on line 1 loads the bump image from a file called logo.gif that is in the same directory as the script file. This image is then converted to an Effect by the code on lines 20 to 24, and placed appropriately relative to the rectangle node to which the lighting effect is applied by using the x and y variables of the Identity class. The lighting itself is a DistantLight, to which the image is supplied as the bump map on line 20.

The image that is used as the bump map is shown on the left of Figure 20-33. The image consists of the word JavaFX in black text on a white background. The white background is actually completely transparent, while the black text is completely opaque. You can see the effect of the bump map on the right of Figure 20-33, where the lighting effect causes the word JavaFX to appear to be raised above the surface of the Rectangle.

Figure 20-33 Using a bump map with a Lighting effect

You can apply the same effect to any node, including an ImageView, where you can use it to create the appearance of a watermark within the image.

DistantLight

The DistantLight class is used when you want to apply a more-or-less uniform light to a node or group. Depending on where the light source is, you may see some shadows, but you will not see reflections of the type that are a characteristic of PointLight and Spotlight, which are discussed in the sections that follow. DistantLight, PointLight, and Spotlight are all derived from the base class javafx.scene.effect.light.Light, which has a single variable called color (of type Color) that specifies the color of the light to be used, which is white by default. The other variables of the DistantLight class specify the position of the light source and are listed in Table 20-19.

Table 20-19. Variables of the DistantLight Class

The azimuth is the position of the light source on the plane of the scene. An azimuth angle of 0 degrees places the light source at the 3 o'clock position, one of 90 degrees moves it to 6 o'clock, and so on. Negative angles can also be used and are measured counterclockwise. For example, setting the azimuth variable to either -90 or 270 places the light source at 12 o'clock.

The elevation gives the angle of the light source above or below the plane of the scene. When the elevation is 0 or 180, the light source is on the plane of the scene, when it is 90, it is overhead the scene and shining directly down on it, and when it is 270 (or -90), it is directly below the scene.

The following code, which you will find in the file javafxeffects/DistantLight1.fx, allows you to move a DistantLight source around a large yellow circle to see the effect that is created:

Circle {
    centerX: 200
    centerY: 180
    radius: 150
    fill: Color.YELLOW
    effect: Lighting {
        light: DistantLight {
            azimuth: bind azimuthSlider.value
            elevation: bind elevationSlider.value
        }
        surfaceScale: 5
    }
}

Figure 20-34 shows two different configurations of the DistantLight source.

Figure 20-34 Using a DistantLight source

On the left of the figure, the azimuth and elevation variables both have the value 45, which places the light source at approximately the 4.30 position and elevated 45 degrees above its surface. You can see that this is the case because the lower-right edge of the circle is much brighter than the rest of it. On the right, the light source has been moved to the 9 o'clock position by setting the azimuth variable to 180 and moved very close to the plane of the scene as a result of the elevation, which is very nearly 0 degrees. Because of the low elevation, most of the circle is quite dark, with the exception of the edge at around the 9 o'clock position, which is closest to the light source.

It is worth examining here the effect of the diffuseConstant of the Lighting class. This constant acts as a multiplier to the RGB values of all the pixels on the lit surface. Therefore, you can use this variable to make the surface lighter or darker. The example in the file javafxeffects/DistantLight2.fx illustrates this by setting the diffuseConstant value of the Lighting effect to 1.5, which has the result of making the circle brighter, as you can see by comparing the result shown in Figure 20-35 with Figure 20-34, where this variable had the value 1.

Figure 20-35 The effect of the diffuseConstant on a lit surface

PointLight

PointLight represents a single point of light that is positioned somewhere relative to the surface to be lit. The variables of the PointLight class, as shown in Table 20-20, allow you to specify exactly where the light source should be placed.

Table 20-20. Variables of the PointLight Class

In the following code, a PointLight source whose position is bound to the values of three sliders is created and applied to a large yellow circle. If you run this example, which can be found in the file javafxeffects/PointLight1.fx, you can experiment with the effect of changing the location of the light source:

Circle {
    centerX: 200
    centerY: 180
    radius: 150
    fill: Color.YELLOW
    effect: Lighting {
        light: PointLight {
            x: bind xSlider.value
            y: bind ySlider.value
            z: bind zSlider.value
        }
        surfaceScale: 5
        specularConstant: bind (specCSlider.value as Number) / 10
        specularExponent: bind specESlider.value
    }
}

You can see two different PointLight configurations in Figure 20-36. On the left, the light is at (x = 45, y = 45, z = 45), which is to the top left of the circle itself. You can see that a PointLight source results in a more concentrated area of illumination than a DistantLight. On the right of the figure, the light source has been moved so that its reflection has moved more toward the center of the circle.

Figure 20-36 Using a PointLight source

The size and intensity of the reflection depends on values of the specularConstant and specularExponent variables of the PointLight class. Like diffuseConstant, specularConstant is a multiplier that is applied to the RGB values of the lit source, so values greater than 1 make the reflection bright, while values less than 1 make it dimmer. The specularExponent controls the spread of the light and therefore the radius of the reflected area. Increasing values of specularExponent reduce this radius and therefore make the reflection brighter. You can see examples that use different settings for these variables in Figure 20-37.

Figure 20-37 The effects of the specularConstant and specularExponent variables

SpotLight

PointLight represents a single-point source of light that shines uniformly in every direction, much like the sun. SpotLight is a subclass of PointLight that acts like a point light source that radiates light over a more confined area. The rays of light are confined to the inside of a cone with its tip at the source. The axis of the cone points to a specified location on the surface of the object being lit. The combination of the position of the light source, the point at which it is aimed, and the width of the cone at the point at which the light reaches the lit object determines the lighting effect that you see. You can specify these values using the variables listed in Table 20-21.

Table 20-21. The Variables of the SpotLight Class

The following code, which is from the file javafxeffects/SpotLight1.fx, applies a SpotLight effect to the same circle that we illuminated with a PointLight source in the previous example. The light source is placed 60 pixels above the center of the circle, while the point at which it is aimed can be controlled by three sliders. The effect produced by the SpotLight with these initial variable settings is shown on the left of Figure 20-38.

Circle {
    centerX: 200
    centerY: 180
    radius: 150
    fill: Color.YELLOW
    effect: Lighting {
        light: SpotLight {
            pointsAtX: bind xSlider.value
            pointsAtY: bind ySlider.value
            pointsAtZ: bind zSlider.value
            x: 200
            y: 180
            z: 60
            specularExponent: bind (specESlider.value as Number)/10
        }
        surfaceScale: 5
    }
}

Figure 20-38 The SpotLight effect

Moving the aiming point changes the resultant lighting effect. When the light source is quite close to the target object, as it is in this case, even a small change in the aiming point can make a noticeable difference to the result. On the right of Figure 20-38, the aiming point has been moved only a small amount to the right and, as you can see, almost half of the circle is now in darkness.

The bottom slider in Figure 20-38 allows you to see the effect of changing the specularExponent value, ⁸ which is initially set to its default value of 1. Increasing this value makes the light cone narrower that produces a more focused beam and therefore a smaller and brighter effect on the target, as you can see in Figure 20-39, where this variable has its maximum value of 4.0. With this setting, almost all the light is confined to a small area around the aiming point.

Figure 20-39 The effect of the specularExponent variable of the SpotLight class