iOS GridView 算法

分享 一段 iOS 中 gridView 实现的算法.

/*
 
 x0     x1      x2      x3
 +-------+-------+-------+ y3
 |       |       |       |
 |   6   |   7   |   8   |
 |       |       |       |
 +-------+-------+-------+ y2
 |       |       |       |
 |   3   |   4   |   5   |
 |       |       |       |
 +-------+-------+-------+ y1
 |       |       |       |
 |   0   |   1   |   2   |
 |       |       |       |
 +-------+-------+-------+ y0
 
 */

#define STRETCH_COORDS(X0, Y0, W, H, TOP, LEFT, BOTTOM, RIGHT) \
	CGFloat x0 = X0; \
	CGFloat x1 = X0 + LEFT; \
	CGFloat x2 = X0 + W - RIGHT; \
	CGFloat x3 = X0 + W; \
	CGFloat y0 = Y0; \
	CGFloat y1 = Y0 + BOTTOM; \
	CGFloat y2 = Y0 + H - TOP; \
	CGFloat y3 = Y0 + H; \
	CGRect r[9]; \
	r[0] = CGRectMake(x0, y0, x1-x0, y1-y0); \
	r[1] = CGRectMake(x1, y0, x2-x1, y1-y0); \
	r[2] = CGRectMake(x2, y0, x3-x2, y1-y0); \
	r[3] = CGRectMake(x0, y1, x1-x0, y2-y1); \
	r[4] = CGRectMake(x1, y1, x2-x1, y2-y1); \
	r[5] = CGRectMake(x2, y1, x3-x2, y2-y1); \
	r[6] = CGRectMake(x0, y2, x1-x0, y3-y2); \
	r[7] = CGRectMake(x1, y2, x2-x1, y3-y2); \
	r[8] = CGRectMake(x2, y2, x3-x2, y3-y2);

- (void)drawInRect:(CGRect)rect blendMode:(CGBlendMode)blendMode alpha:(CGFloat)alpha
{
	CGSize s = self.size;
	CGFloat t = topCapHeight;
	CGFloat l = leftCapWidth;
	
	if(t*2 > s.height-1) t -= 1;
	if(l*2 > s.width-1) l -= 1;
	
	if(_imageRef) {
		if(!_flags.haveSlices) {
			STRETCH_COORDS(0.0, 0.0, s.width, s.height, t, l, t, l)
			#define X(I) slices[I] = [[self upsideDownCrop:r[I]] retain];
			X(0) X(1) X(2)
			X(3) X(4) X(5)
			X(6) X(7) X(8)
			#undef X
			_flags.haveSlices = 1;
		}
		
		CGContextRef ctx = TUIGraphicsGetCurrentContext();
		CGContextSaveGState(ctx);
		CGContextSetAlpha(ctx, alpha);
		CGContextSetBlendMode(ctx, blendMode);
		STRETCH_COORDS(rect.origin.x, rect.origin.y, rect.size.width, rect.size.height, t, l, t, l)
		#define X(I) CGContextDrawImage(ctx, r[I], slices[I].CGImage);
		X(0) X(1) X(2)
		X(3) X(4) X(5)
		X(6) X(7) X(8)
		#undef X
		CGContextRestoreGState(ctx);
	}
}

#undef STRETCH_COORDS