Libgdx之Pixmap

在Android刚开始流行的时候，有一些类似《吹裙子》《擦一擦》之类的小游戏非常火爆。其实他们应用的就是我们这一节所要讲的Pixmap。

Pixmap代表了内存中的图像。Pixmap有高和宽，同时也有指定的格式。Pixmap的坐标系是以左上角开始的，x轴指向右，y轴指向下。默认情况下使用混合渲染的（blending），可以使用方法 setBlending 来开启或者关闭。方法Pixmap.drawPixmap(Pixmap, int, int, int, int, int, int, int, int)将会按比例缩放或者拉伸图像。Pixmap图像存放在堆内存中（native heap memory），不再使用的时候应该调用方法dispose 来销毁防止内存泄露。

其实说白了 Pixmap 就是内存中的图像，但是我们可以对这块图像进行操作，实现一些涂抹的工作，比如实现下面图示的效果:



但是，要想Pixmap真正的在屏幕上显示出来，还需要和Texture结合，才能真正的在屏幕上画出来

下面是一个展示示例：

public class PixmapTest extends ApplicationAdapter {
private static final String TAG = PixmapTest.class.getSimpleName();

SpriteBatch batch;
InputA inputA;
Texture texture;
Pixmap pixmap;
FileHandle file;

@Override
public void create() {
batch = new SpriteBatch();
inputA = new InputA();
Gdx.input.setInputProcessor(inputA);
/**
* RGBA8888 - This is the format we described in the earlier Primer
* section. Each channel (R, G, B, A) is made up of a byte, or 8 bits.
* With this format, we have four bytes per pixel. We would use this for
* high-quality color that requires an alpha channel, for transparency.
* This is known as "True Color". RGB888 - This is similar to the above,
* but discards the alpha channel (i.e. the image is opaque). This is
* useful for high-quality images that don't need an alpha channel.
* RGBA4444 - This is similar to RGBA8888, but stores each channel in
* only 4 bits. This leads to lower color quality, but has performance
* and memory implications on low-end devices like Android and iOS.
* RGB565 - This stores the red channel in 5 bits, the green in 6 bits,
* and the blue in 5 bits. We use an extra bit in the green channel
* since the human eye can generally perceive more gradations of green.
* This is known as "High Color", and is again mainly useful for low-end
* or embedded devices. LuminanceAlpha - This is a grayscale image that
* includes an alpha channel. Grayscale colors have equal red, green and
* blue values, which we call "luminance." So a typical gray value of
* (R=127, G=127, B=127, A=255) would be represented like so with
* LuminanceAlpha: (L=127, A=255). Each uses 8 bits. Alpha - This is a
* special type of image that only stores an alpha channel in 8 bits.
* Intensity - This is another special type of image which only uses a
* single channel, but with the alpha channel equal to the luminance.
* For example, an Intensity color of (I=127) would be equivalent to a
* RGBA color of (R=127, G=127, B=127, A=127).
*/
pixmap = new Pixmap(Gdx.graphics.getWidth(), Gdx.graphics.getHeight(), Pixmap.Format.RGBA4444);

// Fill it red
pixmap.setColor(Color.RED);
pixmap.fill();

// Draw two lines forming an X
pixmap.setColor(Color.BLACK);
pixmap.drawLine(0, 0, pixmap.getWidth() - 1, pixmap.getHeight() - 1);
pixmap.drawLine(0, pixmap.getHeight() - 1, pixmap.getWidth() - 1, 0);

// Draw a circle about the middle
pixmap.setColor(Color.YELLOW);
pixmap.drawCircle(pixmap.getWidth() / 2, pixmap.getHeight() / 2, pixmap.getHeight() / 2 - 1);

//      pixmap = new Pixmap(Gdx.files.internal("badlogic.jpg"));
texture = new Texture(pixmap);

file = Gdx.files.local("bin/img/pixmap.cim");;
}

@Override
public void render() {
Gdx.gl.glClearColor(0.39f, 0.58f, 0.92f, 1.0f);
Gdx.gl.glClear(GL20.GL_COLOR_BUFFER_BIT);

batch.begin();
batch.draw(texture, 0, 0);
batch.end();

}

@Override
public void dispose() {
batch.dispose();
pixmap.dispose();
texture.dispose();
}

class InputA extends InputAdapter {
@Override
public boolean keyTyped(char character) {
switch (character) {
case 's':
PixmapIO.writeCIM(file, pixmap);
Gdx.app.log(TAG, "saved to " + file);
return true;
case 'l':
pixmap.dispose();
if (file.exists()) {
pixmap = PixmapIO.readCIM(file);
texture.draw(pixmap, 0, 0);
Gdx.app.log(TAG, "load from " + file);
} else {
Gdx.app.log(TAG, file + " doesn't exit");
}
return true;
default:
return false;
}
}

@Override
public boolean touchDragged(int screenX, int screenY, int pointer) {
// 定义画笔的颜色
pixmap.setColor(Color.BLUE);
// 画笔其实是一个圆
pixmap.fillCircle(screenX, screenY - (Gdx.graphics.getHeight() - pixmap.getHeight()), 5);
// 将Pixmap和texture相结合
texture.draw(pixmap, 0, 0);
return super.touchDragged(screenX, screenY, pointer);
}
}
}

通过上面代码可以知道，当按键s时可以保存要画的图片，关掉程序，重新启动后，按l可以重新加载绘制的图片。 PixmapIO用来读写图片

如果感觉上面的内容还不够使用的话，可以参考链接， 这里是另外一个例子，希望能更好的帮助你理解。