的OpenLayers旋轉使用precompose當夾層

Question

更新的OpenLayers到後破碎> 4.0地圖使用precompose鉤時旋轉完全破：

function precompose(event) { 
    var context = event.context; 

    context.beginPath(); 
    context.moveTo(0, 0); 
    context.lineTo(100, 0); 
    context.lineTo(100, 100); 
    context.lineTo(0, 100); 
    context.lineTo(0, 0); 
    context.closePath(); 

    context.fillStyle = "rgba(0, 5, 25, 0.75)"; 
    context.fill(); 
} 

Answer 1

它保存畫布背景下，以獲取更多信息是重要見MDN CanvasRenderingContext2d

function precompose(event) { 
    var context = event.context; 
    context.save(); // be sure to save the context before anything is done 
    // ... 
} 

另外，在postcompose鉤使用context.restore()。