我已经创建了一个js函数,该函数应该旋转图像以进行碰撞检测,但是当旋转超过π* 1.5(Pi)时,该函数不能正常工作,图像将被裁剪。
function rotateImage(image , rotation)
{
// Creates a canvas
var rotatedImage = document.createElement( "canvas" ) . getContext( "2d" ),
// Setting a bounding box size
boundingWidth = Math . abs( image . height * Math . cos( rotation ) + image . width * Math . sin( rotation ) ),
boundingHeight = Math . abs( image . height * Math . sin( rotation ) + image . width * Math . cos( rotation ) );
// Changing canvas size
rotatedImage . canvas.width = boundingWidth;
rotatedImage . canvas.height = boundingHeight;
// Translating canvas
rotatedImage . translate( boundingWidth/2 , boundingHeight/2 );
// Rotate canvas
rotatedImage . rotate( rotation );
// Un-translating canvas
rotatedImage . translate( -boundingWidth/2 , -boundingHeight/2 );
// Draws image
rotatedImage . drawImage( image , 0 , 0 );
// Returns canvas
return rotatedImage . canvas;
}
谢谢:)
答案 0 :(得分:3)
[编辑:OP澄清他们想要碰撞检测]
哦......你想要一个旋转矩形的边界框用于碰撞检测。
您不需要使用画布旋转,只需使用三角函数!
// where w = rectangle width (sprite width)
// where h = rectangle height (sprite height)
// where a = angle of rotation in degrees
// calculate the bounding box of the rectangle at the given rotation
function BoundingBoxDimensions(w,h,a){
var rads=a*Math.PI/180;
var c = Math.abs(Math.cos(rads));
var s = Math.abs(Math.sin(rads));
return({ width: h * s + w * c, height: h * c + w * s });
}
关于上面的代码,如果你的Math.sin(旋转)或Math.cos(旋转)变为负数,你需要在BB计算中使用它们之前取其绝对值。这就是为什么你的计算在PI * 1.5上疯狂的原因。