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MID Profile: Class GameCanvas
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javax.microedition.lcdui.game</FONT>
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Class GameCanvas</H2>
<PRE>
<A HREF="../../../../java/lang/Object.html">java.lang.Object</A>
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+--<A HREF="../../../../javax/microedition/lcdui/Displayable.html">javax.microedition.lcdui.Displayable</A>
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+--<A HREF="../../../../javax/microedition/lcdui/Canvas.html">javax.microedition.lcdui.Canvas</A>
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+--<B>javax.microedition.lcdui.game.GameCanvas</B>
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<DT>public abstract class <B>GameCanvas</B><DT>extends <A HREF="../../../../javax/microedition/lcdui/Canvas.html">Canvas</A></DL>
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The GameCanvas class provides the basis for a game user interface. In addition to the features inherited from Canvas (commands, input events, etc.) it also provides game-specific capabilities such as an off-screen graphics buffer and the ability to query key status. <p> A dedicated buffer is created for each GameCanvas instance. Since a unique buffer is provided for each GameCanvas instance, it is preferable to re-use a single GameCanvas instance in the interests of minimizing heap usage. The developer can assume that the contents of this buffer are modified only by calls to the Graphics object(s) obtained from the GameCanvas instance; the contents are not modified by external sources such as other MIDlets or system-level notifications. The buffer is initially filled with white pixels. <p> The buffer's size is set to the maximum dimensions of the GameCanvas. However, the area that may be flushed is limited by the current dimensions of the GameCanvas (as influenced by the presence of a Ticker, Commands, etc.) when the flush is requested. The current dimensions of the GameCanvas may be obtained by calling <A HREF="../../../../javax/microedition/lcdui/Displayable.html#getWidth()"><CODE>getWidth</CODE></A> and <A HREF="../../../../javax/microedition/lcdui/Displayable.html#getHeight()"><CODE>getHeight</CODE></A>. <p> A game may provide its own thread to run the game loop. A typical loop will check for input, implement the game logic, and then render the updated user interface. The following code illustrates the structure of a typcial game loop: <code> <pre> // Get the Graphics object for the off-screen buffer Graphics g = getGraphics(); while (true) { // Check user input and update positions if necessary int keyState = getKeyStates(); if ((keyState & LEFT_PRESSED) != 0) { sprite.move(-1, 0); } else if ((keyState & RIGHT_PRESSED) != 0) { sprite.move(1, 0); } // Clear the background to white g.setColor(0xFFFFFF); g.fillRect(0,0,getWidth(), getHeight()); // Draw the Sprite sprite.paint(g); // Flush the off-screen buffer flushGraphics(); } </pre> </code> <P>
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<DT><B>Since: </B><DD>MIDP 2.0</DD>
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<CODE>static int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../javax/microedition/lcdui/game/GameCanvas.html#DOWN_PRESSED">DOWN_PRESSED</A></B></CODE>
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The bit representing the DOWN key.</TD>
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<CODE>static int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../javax/microedition/lcdui/game/GameCanvas.html#FIRE_PRESSED">FIRE_PRESSED</A></B></CODE>
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The bit representing the FIRE key.</TD>
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<CODE>static int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../javax/microedition/lcdui/game/GameCanvas.html#GAME_A_PRESSED">GAME_A_PRESSED</A></B></CODE>
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The bit representing the GAME_A key (may not be supported on all devices).</TD>
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<CODE>static int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../javax/microedition/lcdui/game/GameCanvas.html#GAME_B_PRESSED">GAME_B_PRESSED</A></B></CODE>
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The bit representing the GAME_B key (may not be supported on all devices).</TD>
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<CODE>static int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../javax/microedition/lcdui/game/GameCanvas.html#GAME_C_PRESSED">GAME_C_PRESSED</A></B></CODE>
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The bit representing the GAME_C key (may not be supported on all devices).</TD>
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<CODE>static int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../javax/microedition/lcdui/game/GameCanvas.html#GAME_D_PRESSED">GAME_D_PRESSED</A></B></CODE>
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The bit representing the GAME_D key (may not be supported on all devices).</TD>
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<CODE>static int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../javax/microedition/lcdui/game/GameCanvas.html#LEFT_PRESSED">LEFT_PRESSED</A></B></CODE>
<BR>
The bit representing the LEFT key.</TD>
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<CODE>static int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../javax/microedition/lcdui/game/GameCanvas.html#RIGHT_PRESSED">RIGHT_PRESSED</A></B></CODE>
<BR>
The bit representing the RIGHT key.</TD>
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<CODE>static int</CODE></FONT></TD>
<TD><CODE><B><A HREF="../../../../javax/microedition/lcdui/game/GameCanvas.html#UP_PRESSED">UP_PRESSED</A></B></CODE>
<BR>
The bit representing the UP key.</TD>
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<TD><B>Fields inherited from class javax.microedition.lcdui.<A HREF="../../../../javax/microedition/lcdui/Canvas.html">Canvas</A></B></TD>
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<TD><CODE><A HREF="../../../../javax/microedition/lcdui/Canvas.html#DOWN">DOWN</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#FIRE">FIRE</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#GAME_A">GAME_A</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#GAME_B">GAME_B</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#GAME_C">GAME_C</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#GAME_D">GAME_D</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#KEY_NUM0">KEY_NUM0</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#KEY_NUM1">KEY_NUM1</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#KEY_NUM2">KEY_NUM2</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#KEY_NUM3">KEY_NUM3</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#KEY_NUM4">KEY_NUM4</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#KEY_NUM5">KEY_NUM5</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#KEY_NUM6">KEY_NUM6</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#KEY_NUM7">KEY_NUM7</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#KEY_NUM8">KEY_NUM8</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#KEY_NUM9">KEY_NUM9</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#KEY_POUND">KEY_POUND</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#KEY_STAR">KEY_STAR</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#LEFT">LEFT</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#RIGHT">RIGHT</A>, <A HREF="../../../../javax/microedition/lcdui/Canvas.html#UP">UP</A></CODE></TD>
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