我想要在画布上绘制图形,使得颜色呈现加法混合。例如,我想要生成这样的效果:
但是,实际上我得到了这个:
请注意,半白半黑的背景是有意为之的,只是为了观察alpha与两种不同背景的交互作用。我希望这段代码能够适用于任何一个背景。以下是我的代码:
public class VennColorsActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
class VennView extends View {
public VennView(Context context) {
super(context);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
int alpha = 60, val = 255;
int ar = Color.argb(alpha, val, 0, 0);
int ag = Color.argb(alpha, 0, val, 0);
int ab = Color.argb(alpha, 0, 0, val);
float w = canvas.getWidth();
float h = canvas.getHeight();
float cx = w / 2f;
float cy = h / 2;
float r = w / 5;
float tx = (float) (r * Math.cos(30 * Math.PI / 180));
float ty = (float) (r * Math.sin(30 * Math.PI / 180));
float expand = 1.5f;
Paint paint = new Paint();
paint.setColor(Color.WHITE);
canvas.drawRect(new Rect(0, 0, (int) w, (int) (h / 2)), paint);
PorterDuff.Mode mode = android.graphics.PorterDuff.Mode.ADD;
paint = new Paint(Paint.ANTI_ALIAS_FLAG);
paint.setColorFilter(new PorterDuffColorFilter(ar, mode));
paint.setColor(ar);
canvas.drawCircle(cx, cy - r, expand * r, paint);
paint.setColorFilter(new PorterDuffColorFilter(ag, mode));
paint.setColor(ag);
canvas.drawCircle(cx - tx, cy + ty, expand * r, paint);
paint.setColorFilter(new PorterDuffColorFilter(ab, mode));
paint.setColor(ab);
canvas.drawCircle(cx + tx, cy + ty, expand * r, paint);
}
}
this.setContentView(new VennView(this));
}
}
请问有人能帮助我理解在Android图形中如何使用加色法绘画吗?