GradientFill.m

// Created by Satoshi Nakagawa.
// You can redistribute it and/or modify it under the Ruby's license or the GPL2.

#import "GradientFill.h"

struct GradientColorInfo
{
  float from[4];
  float to[4];
};

static void interpolate(void* info, float const* in, float* out)
{
  const struct GradientColorInfo* ci = (const struct GradientColorInfo*)info;
  const float* from = ci->from;
  const float* to = ci->to;
  float a = in[0];
  
  int i;
  for (i=0; i<4; i++) {
    out[i] = (1.0 - a) * to[i] + a * from[i];
  }
}

@interface GradientFill (Private)
- (void)setBeginColor:(NSColor*)color;
- (void)setEndColor:(NSColor*)color;
@end

@implementation GradientFill

+ (GradientFill*)gradientWithBeginColor:(NSColor*)from endColor:(NSColor*)end
{
  id gradient = [[GradientFill alloc] init];
  [gradient setBeginColor:from];
  [gradient setEndColor:end];
  return gradient;
}

- (void)dealloc
{
  [beginColor release];
  [endColor release];
  [super dealloc];
}

- (void)setBeginColor:(NSColor*)color
{
  beginColor = [color retain];
}

- (void)setEndColor:(NSColor*)color
{
  endColor = [color retain];
}

- (void)fillRect:(NSRect)rect
{
  struct GradientColorInfo ci;
  ci.from[0] = [beginColor redComponent];
  ci.from[1] = [beginColor greenComponent];
  ci.from[2] = [beginColor blueComponent];
  ci.from[3] = [beginColor alphaComponent];
  ci.to[0] = [endColor redComponent];
  ci.to[1] = [endColor greenComponent];
  ci.to[2] = [endColor blueComponent];
  ci.to[3] = [endColor alphaComponent];
  
  struct CGFunctionCallbacks callbacks = {0, interpolate, NULL};
  CGFunctionRef function = CGFunctionCreate(&ci, 1, NULL, 4, NULL, &callbacks);
  CGColorSpaceRef cspace = CGColorSpaceCreateDeviceRGB();
  CGShadingRef shade = CGShadingCreateAxial(cspace, CGPointMake(NSMinX(rect), NSMaxY(rect)), CGPointMake(NSMinX(rect), NSMinY(rect)), function, false, false);
  CGContextDrawShading([[NSGraphicsContext currentContext] graphicsPort], shade);
  CGShadingRelease(shade);
  CGColorSpaceRelease(cspace);
  CGFunctionRelease(function);
}

@end