Camera预览尺寸和获取屏幕宽高。

算法需要将预览大小与手机的分辨率挂钩，才能够在不同分辨率的手机上面预览都不变形。

/**
* 获取最佳预览大小
* @param parameters 相机参数
* @param screenResolution 屏幕宽高
* @return
*/
private Point getBestCameraResolution(Camera.Parameters parameters, Point screenResolution) {
float tmp = 0f;
float mindiff = 100f;
float x_d_y = (float) screenResolution.x / (float) screenResolution.y;
Size best = null;
List<Size> supportedPreviewSizes = parameters.getSupportedPreviewSizes();
for (Size s : supportedPreviewSizes) {
tmp = Math.abs(((float) s.height / (float) s.width) - x_d_y);
if (tmp < mindiff) {
mindiff = tmp;
best = s;
}
}
return new Point(best.width, best.height);
}

获取屏幕宽高的方法如下：

/**
* 获取屏幕宽度和高度，单位为px
* @param context
* @return
*/
public static Point getScreenMetrics(Context context){
DisplayMetrics dm =context.getResources().getDisplayMetrics();
int w_screen = dm.widthPixels;
int h_screen = dm.heightPixels;
return new Point(w_screen, h_screen);

}