Motorola C370, C550, C450 technical manual GameScreen Methods, Public int getKeyStates

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Gaming API and Sound

•public static final int VOLUME_MIN - The minimum volume for playing sound effects. This constant has a value of 0.

GameScreen Methods

The GameScreen class defines the following methods:

•protected Graphics getGraphics() - Obtains the Graphics object for rendering GameScreens. The Graphics object renders to an off-screen buffer whose size is equal to that of the GameScreen (use getWidth() and getHeight() to determine the size of the GameScreen). The buffer is initially filled with white pixels. Rendering operations do not appear on the display until flushGraphics() is called; flushing the buffer does not change its contents (that is, the pixels are not cleared as a result of the flushing operation). Only one image buffer is supported because without a vertical sync blanking period or its equivalent, there is little or no benefit from having multiple image buffers. Only one Graphics object exists for each GameScreen instance.

•public int getKeyStates() - Gets the states of the physical keys. Each bit in the returned integer represents a specific key on the device. A key's bit will be set if the key is currently pressed or was pressed at least once since the last time this method was called. The bit will be 0 if the key is not currently pressed and was not pressed at all since the last time this method was called. This latching behavior ensures that a rapid key press and release will always be caught by the game loop, regardless of how slowly the loop runs. This method may be called twice to check if a key is currently pressed; that is, calling this method twice effectively disables the latching behavior. The lower bits are defined by UP_KEY, DOWN_KEY, LEFT_KEY, etc.; the remaining bits may be mapped to device-specific keys.

The following is a code sample to show implementation of public int getKeyStates():

Public int getKeyStates ()

// Get the key state and store it

int keyState = gameScreenObject.getKeyStates(); if ((keyState & LEFT_KEY) != 0) {

positionX--;

} else if ((keyState & RIGHT_KEY) != 0) { positionX++;

}

•public void enableKeyEvents(boolean enabled) - Enables or disables key event calls to this GameScreen. If disabled, the Canvas key event methods (keyPressed, keyRepeated, keyReleased) are not called when keys are pressed or released; however, the developer can still call getKeyStates to query the state of the keys. For games that poll key state and do not need event-driven key

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