javax.microedition.lcdui.game
Class Sprite

java.lang.Object

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  +--javax.microedition.lcdui.game.Layer

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        +--javax.microedition.lcdui.game.Sprite

public class Sprite

extends Layer

A Sprite is a basic visual element that can be rendered with one of several frames stored in an Image; different frames can be shown to animate the Sprite. Several transforms such as flipping and rotation can also be applied to a Sprite to further vary its appearance. As with all Layer subclasses, a Sprite's location can be changed and it can also be made visible or invisible.

Sprite Frames

The raw frames used to render a Sprite are provided in a single Image object, which may be mutable or immutable. If more than one frame is used, the Image is broken up into a series of equally-sized frames of a specified width and height. As shown in the figure below, the same set of frames may be stored in several different arrangements depending on what is the most convenient for the game developer.

Each frame is assigned a unique index number. The frame located in the upper-left corner of the Image is assigned an index of 0. The remaining frames are then numbered consecutively in row-major order (indices are assigned across the first row, then the second row, and so on). The method getRawFrameCount() returns the total number of raw frames.

Frame Sequence

A Sprite's frame sequence defines an ordered list of frames to be displayed. The default frame sequence mirrors the list of available frames, so there is a direct mapping between the sequence index and the corresponding frame index. This also means that the length of the default frame sequence is equal to the number of raw frames. For example, if a Sprite has 4 frames, its default frame sequence is {0, 1, 2, 3}.

The developer must manually switch the current frame in the frame sequence. This may be accomplished by calling setFrame(int), prevFrame(), or nextFrame(). Note that these methods always operate on the sequence index, they do not operate on frame indices; however, if the default frame sequence is used, then the sequence indices and the frame indices are interchangeable.

If desired, an arbitrary frame sequence may be defined for a Sprite. The frame sequence must contain at least one element, and each element must reference a valid frame index. By defining a new frame sequence, the developer can conveniently display the Sprite's frames in any order desired; frames may be repeated, omitted, shown in reverse order, etc.

For example, the diagram below shows how a special frame sequence might be used to animate a mosquito. The frame sequence is designed so that the mosquito flaps its wings three times and then pauses for a moment before the cycle is repeated.

By calling nextFrame() each time the display is updated, the resulting animation would like this:

Reference Pixel

Being a subclass of Layer, Sprite inherits various methods for setting and retrieving its location such as setPosition(x,y), getX(), and getY(). These methods all define position in terms of the upper-left corner of the Sprite's visual bounds; however, in some cases, it is more convenient to define the Sprite's position in terms of an arbitrary pixel within its frame, especially if transforms are applied to the Sprite.

Therefore, Sprite includes the concept of a reference pixel. The reference pixel is defined by specifying its location in the Sprite's untransformed frame using defineReferencePixel(x,y). By default, the reference pixel is defined to be the pixel at (0,0) in the frame. If desired, the reference pixel may be defined outside of the frame's bounds.

In this example, the reference pixel is defined to be the pixel that the monkey appears to be hanging from:

getRefPixelX() and getRefPixelY() can be used to query the location of the reference pixel in the painter's coordinate system. The developer can also use setRefPixelPosition(x,y) to position the Sprite so that reference pixel appears at a specific location in the painter's coordinate system. These methods automatically account for any transforms applied to the Sprite.

In this example, the reference pixel's position is set to a point at the end of a tree branch; the Sprite's location changes so that the reference pixel appears at this point and the monkey appears to be hanging from the branch:

Sprite Transforms

Various transforms can be applied to a Sprite. The available transforms include rotations in multiples of 90 degrees, and mirrored (about the vertical axis) versions of each of the rotations. A Sprite's transform is set by calling setTransform(transform).

When a transform is applied, the Sprite is automatically repositioned such that the reference pixel appears stationary in the painter's coordinate system. Thus, the reference pixel effectively becomes the center of the transform operation. Since the reference pixel does not move, the values returned by getRefPixelX() and getRefPixelY() remain the same; however, the values returned by getX() and getY() may change to reflect the movement of the Sprite's upper-left corner.

Referring to the monkey example once again, the position of the reference pixel remains at (48, 22) when a 90 degree rotation is applied, thereby making it appear as if the monkey is swinging from the branch:

Sprite Drawing

Sprites can be drawn at any time using the paint(Graphics) method. The Sprite will be drawn on the Graphics object according to the current state information maintained by the Sprite (i.e. position, frame, visibility). Erasing the Sprite is always the responsibility of code outside the Sprite class.

Sprites can be implemented using whatever techniques a manufacturers wishes to use (e.g hardware acceleration may be used for all Sprites, for certain sizes of Sprites, or not at all).

For some platforms, certain Sprite sizes may be more efficient than others; manufacturers may choose to provide developers with information about device-specific characteristics such as these.

Since:

MIDP 2.0

Field Summary

static int	TRANS_MIRROR Causes the Sprite to appear reflected about its vertical center.
static int	TRANS_MIRROR_ROT180 Causes the Sprite to appear reflected about its vertical center and then rotated clockwise by 180 degrees.
static int	TRANS_MIRROR_ROT270 Causes the Sprite to appear reflected about its vertical center and then rotated clockwise by 270 degrees.
static int	TRANS_MIRROR_ROT90 Causes the Sprite to appear reflected about its vertical center and then rotated clockwise by 90 degrees.
static int	TRANS_NONE No transform is applied to the Sprite.
static int	TRANS_ROT180 Causes the Sprite to appear rotated clockwise by 180 degrees.
static int	TRANS_ROT270 Causes the Sprite to appear rotated clockwise by 270 degrees.
static int	TRANS_ROT90 Causes the Sprite to appear rotated clockwise by 90 degrees.

Constructor Summary

Sprite(Image image)
Creates a new non-animated Sprite using the provided Image.

Sprite(Image image, int frameWidth, int frameHeight)
Creates a new animated Sprite using frames contained in the provided Image.

Sprite(Sprite s)
Creates a new Sprite from another Sprite.

Method Summary

boolean	collidesWith(Image image, int x, int y, boolean pixelLevel) Checks for a collision between this Sprite and the specified Image with its upper left corner at the specified location.
boolean	collidesWith(Sprite s, boolean pixelLevel) Checks for a collision between this Sprite and the specified Sprite.
boolean	collidesWith(TiledLayer t, boolean pixelLevel) Checks for a collision between this Sprite and the specified TiledLayer.
void	defineCollisionRectangle(int x, int y, int width, int height) Defines the Sprite's bounding rectangle that is used for collision detection purposes.
void	defineReferencePixel(int x, int y) Defines the reference pixel for this Sprite.
int	getFrame() Gets the current index in the frame sequence.
int	getFrameSequenceLength() Gets the number of elements in the frame sequence.
int	getRawFrameCount() Gets the number of raw frames for this Sprite.
int	getRefPixelX() Gets the horizontal position of this Sprite's reference pixel in the painter's coordinate system.
int	getRefPixelY() Gets the vertical position of this Sprite's reference pixel in the painter's coordinate system.
void	nextFrame() Selects the next frame in the frame sequence.
void	paint(Graphics g) Draws the Sprite.
void	prevFrame() Selects the previous frame in the frame sequence.
void	setFrame(int sequenceIndex) Selects the current frame in the frame sequence.
void	setFrameSequence(int[] sequence) Set the frame sequence for this Sprite.
void	setImage(Image img, int frameWidth, int frameHeight) Changes the Image containing the Sprite's frames.
void	setRefPixelPosition(int x, int y) Sets this Sprite's position such that its reference pixel is located at (x,y) in the painter's coordinate system.
void	setTransform(int transform) Sets the transform for this Sprite.

Methods inherited from class javax.microedition.lcdui.game.Layer

getHeight, getWidth, getX, getY, isVisible, move, setPosition, setVisible

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

TRANS_NONE

public static final int TRANS_NONE

No transform is applied to the Sprite. This constant has a value of 0.

TRANS_ROT90

public static final int TRANS_ROT90

Causes the Sprite to appear rotated clockwise by 90 degrees. This constant has a value of 5.

TRANS_ROT180

public static final int TRANS_ROT180

Causes the Sprite to appear rotated clockwise by 180 degrees. This constant has a value of 3.

TRANS_ROT270

public static final int TRANS_ROT270

Causes the Sprite to appear rotated clockwise by 270 degrees. This constant has a value of 6.

TRANS_MIRROR

public static final int TRANS_MIRROR

Causes the Sprite to appear reflected about its vertical center. This constant has a value of 2.

TRANS_MIRROR_ROT90

public static final int TRANS_MIRROR_ROT90

Causes the Sprite to appear reflected about its vertical center and then rotated clockwise by 90 degrees. This constant has a value of 7.

TRANS_MIRROR_ROT180

public static final int TRANS_MIRROR_ROT180

Causes the Sprite to appear reflected about its vertical center and then rotated clockwise by 180 degrees. This constant has a value of 1.

TRANS_MIRROR_ROT270

public static final int TRANS_MIRROR_ROT270

Causes the Sprite to appear reflected about its vertical center and then rotated clockwise by 270 degrees. This constant has a value of 4.

Constructor Detail

Sprite

public Sprite(Image image)

Creates a new non-animated Sprite using the provided Image. This constructor is functionally equivalent to calling new Sprite(image, image.getWidth(), image.getHeight())

By default, the Sprite is visible and its upper-left corner is positioned at (0,0) in the painter's coordinate system.

Parameters:

image - the Image to use as the single frame for the Sprite

Throws:

NullPointerException - if img is null

Sprite

public Sprite(Image image,
              int frameWidth,
              int frameHeight)

Creates a new animated Sprite using frames contained in the provided Image. The frames must be equally sized, with the dimensions specified by frameWidth and frameHeight. They may be laid out in the image horizontally, vertically, or as a grid. The width of the source image must be an integer multiple of the frame width, and the height of the source image must be an integer multiple of the frame height. The values returned by Layer.getWidth() and Layer.getHeight() will reflect the frame width and frame height subject to the Sprite's current transform.

Sprites have a default frame sequence corresponding to the raw frame numbers, starting with frame 0. The frame sequence may be modified with setFrameSequence(int[]).

By default, the Sprite is visible and its upper-left corner is positioned at (0,0) in the painter's coordinate system.

Parameters:

image - the Image to use for Sprite

frameWidth - the width, in pixels, of the individual raw frames

frameHeight - the height, in pixels, of the individual raw frames

Throws:

NullPointerException - if img is null

IllegalArgumentException - if frameHeight or frameWidth is less than 1

IllegalArgumentException - if the image width is not an integer multiple of the frameWidth

IllegalArgumentException - if the image height is not an integer multiple of the frameHeight

Sprite

public Sprite(Sprite s)

Creates a new Sprite from another Sprite.

All instance attributes (raw frames, position, frame sequence, current frame, reference point, collision rectangle, transform, and visibility) of the source Sprite are duplicated in the new Sprite.

Parameters:

s - the Sprite to create a copy of

Throws:

NullPointerException - if s is null

Method Detail

defineReferencePixel

public void defineReferencePixel(int x,
                                 int y)

Defines the reference pixel for this Sprite. The pixel is defined by its location relative to the upper-left corner of the Sprite's un-transformed frame, and it may lay outside of the frame's bounds.

When a transformation is applied, the reference pixel is defined relative to the Sprite's initial upper-left corner before transformation. This corner may no longer appear as the upper-left corner in the painter's coordinate system under current transformation.

By default, a Sprite's reference pixel is located at (0,0); that is, the pixel in the upper-left corner of the raw frame.

Changing the reference pixel does not change the Sprite's physical position in the painter's coordinate system; that is, the values returned by getX() and getY() will not change as a result of defining the reference pixel. However, subsequent calls to methods that involve the reference pixel will be impacted by its new definition.

Parameters:

x - the horizontal location of the reference pixel, relative to the left edge of the un-transformed frame

y - the vertical location of the reference pixel, relative to the top edge of the un-transformed frame

See Also:

setRefPixelPosition(int, int), getRefPixelX(), getRefPixelY()

setRefPixelPosition

public void setRefPixelPosition(int x,
                                int y)

Sets this Sprite's position such that its reference pixel is located at (x,y) in the painter's coordinate system.

Parameters:

x - the horizontal location at which to place the reference pixel

y - the vertical location at which to place the reference pixel

See Also:

defineReferencePixel(int, int), getRefPixelX(), getRefPixelY()

getRefPixelX

public int getRefPixelX()

Gets the horizontal position of this Sprite's reference pixel in the painter's coordinate system.

Returns:

the horizontal location of the reference pixel

See Also:

defineReferencePixel(int, int), setRefPixelPosition(int, int), getRefPixelY()

getRefPixelY

public int getRefPixelY()

Gets the vertical position of this Sprite's reference pixel in the painter's coordinate system.

Returns:

the vertical location of the reference pixel

See Also:

defineReferencePixel(int, int), setRefPixelPosition(int, int), getRefPixelX()

setFrame

public void setFrame(int sequenceIndex)

Selects the current frame in the frame sequence.

The current frame is rendered when paint(Graphics) is called.

The index provided refers to the desired entry in the frame sequence, not the index of the actual frame itself.

Parameters:

sequenceIndex - the index of of the desired entry in the frame sequence

Throws:

IndexOutOfBoundsException - if frameIndex is less than0

IndexOutOfBoundsException - if frameIndex is equal to or greater than the length of the current frame sequence (or the number of raw frames for the default sequence)

See Also:

setFrameSequence(int[]), getFrame()

getFrame

public final int getFrame()

Gets the current index in the frame sequence.

The index returned refers to the current entry in the frame sequence, not the index of the actual frame that is displayed.

Returns:

the current index in the frame sequence

See Also:

setFrameSequence(int[]), setFrame(int)

getRawFrameCount

public int getRawFrameCount()

Gets the number of raw frames for this Sprite. The value returned reflects the number of frames; it does not reflect the length of the Sprite's frame sequence. However, these two values will be the same if the default frame sequence is used.

Returns:

the number of raw frames for this Sprite

See Also:

getFrameSequenceLength()

getFrameSequenceLength

public int getFrameSequenceLength()

Gets the number of elements in the frame sequence. The value returned reflects the length of the Sprite's frame sequence; it does not reflect the number of raw frames. However, these two values will be the same if the default frame sequence is used.

Returns:

the number of elements in this Sprite's frame sequence

See Also:

getRawFrameCount()

nextFrame

public void nextFrame()

Selects the next frame in the frame sequence.

The frame sequence is considered to be circular, i.e. if nextFrame() is called when at the end of the sequence, this method will advance to the first entry in the sequence.

See Also:

setFrameSequence(int[]), prevFrame()

prevFrame

public void prevFrame()

Selects the previous frame in the frame sequence.

The frame sequence is considered to be circular, i.e. if prevFrame() is called when at the start of the sequence, this method will advance to the last entry in the sequence.

See Also:

setFrameSequence(int[]), nextFrame()

paint

public final void paint(Graphics g)

Draws the Sprite.

Draws current frame of Sprite using the provided Graphics object. The Sprite's upper left corner is rendered at the Sprite's current position relative to the origin of the Graphics object. The current position of the Sprite's upper-left corner can be retrieved by calling Layer.getX() and Layer.getY().

Rendering is subject to the clip region of the Graphics object. The Sprite will be drawn only if it is visible.

If the Sprite's Image is mutable, the Sprite is rendered using the current contents of the Image.

Overrides:

paint in class Layer

Parameters:

g - the graphics object to draw Sprite on

Throws:

NullPointerException - if g is null

setFrameSequence

public void setFrameSequence(int[] sequence)

Set the frame sequence for this Sprite.

All Sprites have a default sequence that displays the Sprites frames in order. This method allows for the creation of an arbitrary sequence using the available frames. The current index in the frame sequence is reset to zero as a result of calling this method.

The contents of the sequence array are copied when this method is called; thus, any changes made to the array after this method returns have no effect on the Sprite's frame sequence.

Passing in null causes the Sprite to revert to the default frame sequence.

Parameters:

sequence - an array of integers, where each integer represents a frame index

Throws:

ArrayIndexOutOfBoundsException - if seq is non-null and any member of the array has a value less than 0 or greater than or equal to the number of frames as reported by getRawFrameCount()

IllegalArgumentException - if the array has less than 1 element

See Also:

nextFrame(), prevFrame(), setFrame(int), getFrame()

setImage

public void setImage(Image img,
                     int frameWidth,
                     int frameHeight)

Changes the Image containing the Sprite's frames.

Replaces the current raw frames of the Sprite with a new set of raw frames. See the constructor Sprite(Image, int, int) for information on how the frames are created from the image. The values returned by Layer.getWidth() and Layer.getHeight() will reflect the new frame width and frame height subject to the Sprite's current transform.

Changing the image for the Sprite could change the number of raw frames. If the new frame set has as many or more raw frames than the previous frame set, then:

• The current frame will be unchanged
• If a custom frame sequence has been defined (using setFrameSequence(int[])), it will remain unchanged. If no custom frame sequence is defined (i.e. the default frame sequence is in use), the default frame sequence will be updated to be the default frame sequence for the new frame set. In other words, the new default frame sequence will include all of the frames from the new raw frame set, as if this new image had been used in the constructor.

If the new frame set has fewer frames than the previous frame set, then:

• The current frame will be reset to entry 0
• Any custom frame sequence will be discarded and the frame sequence will revert to the default frame sequence for the new frame set.

The reference point location is unchanged as a result of calling this method, both in terms of its defined location within the Sprite and its position in the painter's coordinate system. However, if the frame size is changed and the Sprite has been transformed, the position of the Sprite's upper-left corner may change such that the reference point remains stationary.

If the Sprite's frame size is changed by this method, the collision rectangle is reset to its default value (i.e. it is set to the new bounds of the untransformed Sprite).

Parameters:

img - the Image to use for Sprite

frameWidth - the width in pixels of the individual raw frames

frameHeight - the height in pixels of the individual raw frames

Throws:

NullPointerException - if img is null

IllegalArgumentException - if frameHeight or frameWidth is less than 1

IllegalArgumentException - if the image width is not an integer multiple of the frameWidth

IllegalArgumentException - if the image height is not an integer multiple of the frameHeight

defineCollisionRectangle

public void defineCollisionRectangle(int x,
                                     int y,
                                     int width,
                                     int height)

Defines the Sprite's bounding rectangle that is used for collision detection purposes. This rectangle is specified relative to the un-transformed Sprite's upper-left corner and defines the area that is checked for collision detection. For pixel-level detection, only those pixels within the collision rectangle are checked. By default, a Sprite's collision rectangle is located at 0,0 as has the same dimensions as the Sprite. The collision rectangle may be specified to be larger or smaller than the default rectangle; if made larger, the pixels outside the bounds of the Sprite are considered to be transparent for pixel-level collision detection.

Parameters:

x - the horizontal location of the collision rectangle relative to the untransformed Sprite's left edge

y - the vertical location of the collision rectangle relative to the untransformed Sprite's top edge

width - the width of the collision rectangle

height - the height of the collision rectangle

Throws:

IllegalArgumentException - if the specified width or height is less than 0

setTransform

public void setTransform(int transform)

Sets the transform for this Sprite. Transforms can be applied to a Sprite to change its rendered appearance. Transforms are applied to the original Sprite image; they are not cumulative, nor can they be combined. By default, a Sprite's transform is TRANS_NONE.

Since some transforms involve rotations of 90 or 270 degrees, their use may result in the overall width and height of the Sprite being swapped. As a result, the values returned by Layer.getWidth() and Layer.getHeight() may change.

The collision rectangle is also modified by the transform so that it remains static relative to the pixel data of the Sprite. Similarly, the defined reference pixel is unchanged by this method, but its visual location within the Sprite may change as a result.

This method repositions the Sprite so that the location of the reference pixel in the painter's coordinate system does not change as a result of changing the transform. Thus, the reference pixel effectively becomes the centerpoint for the transform. Consequently, the values returned by getRefPixelX() and getRefPixelY() will be the same both before and after the transform is applied, but the values returned by getX() and getY() may change.

Parameters:

transform - the desired transform for this Sprite

Throws:

IllegalArgumentException - if the requested transform is invalid

See Also:

TRANS_NONE, TRANS_ROT90, TRANS_ROT180, TRANS_ROT270, TRANS_MIRROR, TRANS_MIRROR_ROT90, TRANS_MIRROR_ROT180, TRANS_MIRROR_ROT270

collidesWith

public final boolean collidesWith(Sprite s,
                                  boolean pixelLevel)

Checks for a collision between this Sprite and the specified Sprite.

If pixel-level detection is used, a collision is detected only if opaque pixels collide. That is, an opaque pixel in the first Sprite would have to collide with an opaque pixel in the second Sprite for a collision to be detected. Only those pixels within the Sprites' respective collision rectangles are checked.

If pixel-level detection is not used, this method simply checks if the Sprites' collision rectangles intersect.

Any transforms applied to the Sprites are automatically accounted for.

Both Sprites must be visible in order for a collision to be detected.

Parameters:

s - the Sprite to test for collision with

pixelLevel - true to test for collision on a pixel-by-pixel basis, false to test using simple bounds checking.

Returns:

true if the two Sprites have collided, otherwise false

Throws:

NullPointerException - if Sprite s is null

collidesWith

public final boolean collidesWith(TiledLayer t,
                                  boolean pixelLevel)

Checks for a collision between this Sprite and the specified TiledLayer. If pixel-level detection is used, a collision is detected only if opaque pixels collide. That is, an opaque pixel in the Sprite would have to collide with an opaque pixel in TiledLayer for a collision to be detected. Only those pixels within the Sprite's collision rectangle are checked.

If pixel-level detection is not used, this method simply checks if the Sprite's collision rectangle intersects with a non-empty cell in the TiledLayer.

Any transform applied to the Sprite is automatically accounted for.

The Sprite and the TiledLayer must both be visible in order for a collision to be detected.

Parameters:

t - the TiledLayer to test for collision with

pixelLevel - true to test for collision on a pixel-by-pixel basis, false to test using simple bounds checking against non-empty cells.

Returns:

true if this Sprite has collided with the TiledLayer, otherwise false

Throws:

NullPointerException - if t is null

collidesWith

public final boolean collidesWith(Image image,
                                  int x,
                                  int y,
                                  boolean pixelLevel)

Checks for a collision between this Sprite and the specified Image with its upper left corner at the specified location. If pixel-level detection is used, a collision is detected only if opaque pixels collide. That is, an opaque pixel in the Sprite would have to collide with an opaque pixel in Image for a collision to be detected. Only those pixels within the Sprite's collision rectangle are checked.

If pixel-level detection is not used, this method simply checks if the Sprite's collision rectangle intersects with the Image's bounds.

Any transform applied to the Sprite is automatically accounted for.

The Sprite must be visible in order for a collision to be detected.

Parameters:

image - the Image to test for collision

x - the horizontal location of the Image's upper left corner

y - the vertical location of the Image's upper left corner

pixelLevel - true to test for collision on a pixel-by-pixel basis, false to test using simple bounds checking

Returns:

true if this Sprite has collided with the Image, otherwise false

Throws:

NullPointerException - if image is null