Core Graphics中的精确像素网格叠加？
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在创建以像素为中心的图像编辑器的实验中，我一直试图绘制精确的网格覆盖图，以帮助引导用户尝试访问某些像素。但是，我绘制的网格不是很均匀，特别是在较小的尺寸下。这是一种常规模式，每隔几列普通列都会增加一个稍大的列，因此我认为这是一个舍入问题，但是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);
}
}
}
没有找到相关结果
已邀请:
1 个回复
佩疵瓦
您想从像素的中心进行绘制，因为否则，您的线会跨越两个像素。 换句话说，在设置xPoints和yPoints的位置，请确保将floor（）或round（）设置为您的值，然后添加0.5。