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Draw a color wheel in Objective-C
//
// DPColorPickerView.m
// DMXPerformer
//
// Created by Phil Christensen on 4/14/13.
// Copyright (c) 2013 bubblehouse. All rights reserved.
//
#import "DPColorPickerView.h"
#import "DPColorGrabberView.h"
#import <CoreFoundation/CoreFoundation.h>
@implementation DPColorPickerView
@synthesize luminance;
// http://stackoverflow.com/questions/5108921/how-to-draw-a-color-wheel-in-objective-c
void generateColorWheelBitmap(UInt8 *bitmap, int widthHeight, float l){
// I think maybe you can do 1/3 of the pie, then do something smart to generate the other two parts, but for now we'll brute force it.
for (int y = 0; y < widthHeight; y++){
for (int x = 0; x < widthHeight; x++){
float h, s, r, g, b, a;
getColorWheelValue(widthHeight, x, y, &h, &s);
if (s < 1.0){
// Antialias the edge of the circle.
if (s > 0.99) a = (1.0 - s) * 100;
else a = 1.0;
HSL2RGB(h, s, l, &r, &g, &b);
}
else {
r = g = b = a = 0.0f;
}
int i = 4 * (x + y * widthHeight);
bitmap[i] = r * 0xff;
bitmap[i+1] = g * 0xff;
bitmap[i+2] = b * 0xff;
bitmap[i+3] = a * 0xff;
}
}
}
void getColorWheelValue(int widthHeight, int x, int y, float *outH, float *outS){
int c = widthHeight / 2;
float dx = (float)(x - c) / c;
float dy = (float)(y - c) / c;
float d = sqrtf((float)(dx*dx + dy*dy));
*outS = d;
*outH = acosf((float)dx / d) / M_PI / 2.0f;
if (dy < 0) *outH = 1.0 - *outH;
}
UIImage *createUIImageWithRGBAData(CFDataRef data, int width, int height){
CGDataProviderRef dataProvider = CGDataProviderCreateWithCFData(data);
CGColorSpaceRef colorSpace = CGColorSpaceCreateDeviceRGB();
CGImageRef imageRef = CGImageCreate(width, height, 8, 32, width * 4, colorSpace, (CGBitmapInfo)kCGImageAlphaLast, dataProvider, NULL, 0, kCGRenderingIntentDefault);
UIImage *image = [[UIImage alloc] initWithCGImage:imageRef];
CGDataProviderRelease(dataProvider);
CGColorSpaceRelease(colorSpace);
CGImageRelease(imageRef);
return image;
}
// Adapted from Apple sample code. See http://en.wikipedia.org/wiki/HSV_color_space#Comparison_of_HSL_and_HSV
void HSL2RGB(float h, float s, float l, float* outR, float* outG, float* outB){
float temp1, temp2;
float temp[3];
int i;
// Check for saturation. If there isn't any just return the luminance value for each, which results in gray.
if(s == 0.0){
*outR = l;
*outG = l;
*outB = l;
return;
}
// Test for luminance and compute temporary values based on luminance and saturation
if(l < 0.5)
temp2 = l * (1.0 + s);
else
temp2 = l + s - l * s;
temp1 = 2.0 * l - temp2;
// Compute intermediate values based on hue
temp[0] = h + 1.0 / 3.0;
temp[1] = h;
temp[2] = h - 1.0 / 3.0;
for(i = 0; i < 3; ++i){
// Adjust the range
if(temp[i] < 0.0)
temp[i] += 1.0;
if(temp[i] > 1.0)
temp[i] -= 1.0;
if(6.0 * temp[i] < 1.0)
temp[i] = temp1 + (temp2 - temp1) * 6.0 * temp[i];
else {
if(2.0 * temp[i] < 1.0)
temp[i] = temp2;
else {
if(3.0 * temp[i] < 2.0)
temp[i] = temp1 + (temp2 - temp1) * ((2.0 / 3.0) - temp[i]) * 6.0;
else
temp[i] = temp1;
}
}
}
// Assign temporary values to R, G, B
*outR = temp[0];
*outG = temp[1];
*outB = temp[2];
}
- (UIColor*)getColorAtX:(int)xx andY:(int)yy {
float h, s;
getColorWheelValue(self.bounds.size.width, xx, yy, &h, &s);
float r, g, b;
HSL2RGB(h, s, self.luminance, &r, &g, &b);
return [UIColor colorWithRed:r green:g blue:b alpha:1];
}
- (id)initWithFrame:(CGRect)frame {
self = [super initWithFrame:frame];
if (self) {
// Initialization code
}
return self;
}
- (void)awakeFromNib {
self.luminance = 0.5;
}
- (void)drawRect:(CGRect)rect {
int dim = self.bounds.size.width; // should always be square.
CFMutableDataRef bitmapData = CFDataCreateMutable(NULL, 0);
CFDataSetLength(bitmapData, dim * dim * 4);
generateColorWheelBitmap(CFDataGetMutableBytePtr(bitmapData), dim, self.luminance);
self.image = createUIImageWithRGBAData(bitmapData, self.bounds.size.width, self.bounds.size.height);
CFRelease(bitmapData);
[self.image drawAtPoint:CGPointZero];
}
@end
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