在创建以像素为中心的图像编辑器的实验中,我一直在尝试绘制精确的网格覆盖,以帮助指导用户访问某些像素。然而,我画的网格不是很均匀,尤其是在较小的尺寸下。这是一种规则模式,每隔几个正常列就有一个稍大的列,所以我认为这是一个舍入问题,但我在代码中看不到它。这是我的代码:
- (void)drawRect:(NSRect)dirtyRect
{
context = [[NSGraphicsContext currentContext] graphicsPort];
CGContextAddRect(context, NSRectToCGRect(self.bounds));
CGContextSetRGBStrokeColor(context, 1.0f, 0.0f, 0.0f, 1.0f);
CGContextStrokePath(context);
CGContextSetInterpolationQuality(context, kCGInterpolationNone);
CGContextSetShouldAntialias(context, NO);
if (image)
{
NSRect imageRect = NSZeroRect;
imageRect.size = CGImageGetSize([image CGImage]);
drawRect = [self bounds];
NSRect viewRect = drawRect;
CGFloat aspectRatio = imageRect.size.width / imageRect.size.height;
if (viewRect.size.width / viewRect.size.height <= aspectRatio)
{
drawRect.size.width = viewRect.size.width;
drawRect.size.height = imageRect.size.height * (viewRect.size.width / imageRect.size.width);
}
else
{
drawRect.size.height = viewRect.size.height;
drawRect.size.width = imageRect.size.width * (viewRect.size.height / imageRect.size.height);
}
drawRect.origin.x += (viewRect.size.width - drawRect.size.width) / 2.0;
drawRect.origin.y += (viewRect.size.height - drawRect.size.height) / 2.0;
CGContextDrawImage(context, drawRect, [image CGImage]);
if (showPixelGrid)
{
//Draw grid by creating start and end points for vertical and horizontal lines.
//FIXME: Grid is uneven, especially at smaller sizes.
CGContextSetStrokeColorWithColor(context, CGColorGetConstantColor(kCGColorBlack));
CGContextAddRect(context, drawRect);
CGContextStrokePath(context);
NSUInteger numXPoints = (NSUInteger)imageRect.size.width * 2;
NSUInteger numYPoints = (NSUInteger)imageRect.size.height * 2;
CGPoint xPoints[numXPoints];
CGPoint yPoints[numYPoints];
CGPoint startPoint;
CGPoint endPoint;
CGFloat widthRatio = drawRect.size.width / imageRect.size.width;
CGFloat heightRatio = drawRect.size.height / imageRect.size.height;
startPoint.x = drawRect.origin.x;
startPoint.y = drawRect.origin.y;
endPoint.x = drawRect.origin.x;
endPoint.y = drawRect.size.height + drawRect.origin.y;
for (NSUInteger i = 0; i < numXPoints; i += 2)
{
startPoint.x += widthRatio;
endPoint.x += widthRatio;
xPoints[i] = startPoint;
xPoints[i + 1] = endPoint;
}
startPoint.x = drawRect.origin.x;
startPoint.y = drawRect.origin.y;
endPoint.x = drawRect.size.width + drawRect.origin.x;
endPoint.y = drawRect.origin.y;
for (NSUInteger i = 0; i < numYPoints; i += 2)
{
startPoint.y += heightRatio;
endPoint.y += heightRatio;
yPoints[i] = startPoint;
yPoints[i + 1] = endPoint;
}
CGContextStrokeLineSegments(context, xPoints, numXPoints);
CGContextStrokeLineSegments(context, yPoints, numYPoints);
}
}
}
有什么想法吗?
更新:我设法通过一些调整使您的代码运行-CGImageGetSize()从哪里来?-我真的看不出有什么问题,除了列并不是都是非常小的尺寸。这就是它的工作原理。解决这一问题的唯一方法是将缩放比例固定为图像大小的整数倍,换句话说,使图像大小的最大整数倍小于视图大小,或者减少在屏幕上以非常小的尺寸绘制的线的数量,以消除这种伪影。在大多数编辑器中,像素网格只有在长距离缩放时才可见,这是有原因的。更不用说,如果网格在3-4倍的分辨率下仍然可见,那么视图就太忙了。
我无法运行您提供的代码,因为其中有一堆类ivar,但粗略地看,我认为这与绘制像素边界有关。在你四舍五入到一个整数以消除模糊的AA伪影(我注意到你关闭了AA,但理想情况下你不应该这样做)之后,你需要在原点上加0.5,以使你的线绘制在像素的中心上,而不是边界。
像这样:
+---X---+---+---+---+---+
| | | | Y | | |
+---+---+---+---+---+---+
X : CGPoint (1, 1)
Y : CGPoint (3.5, 0.5)
您希望从像素的中心绘制,因为否则您的线将横跨两个像素。
换言之,在设置xPoints和yPoints的地方,确保对值进行floor()或round(),然后加0.5。