arcs.c

/*
 
 File: arcs.c
 
 Abstract: //   These are the functions that implement equivalents to the QuickDraw arc drawing APIs,
           //   FrameArc and PaintArc.
           //   See DrawProcs.c for sample usage
 
 Version: 1.0
 
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 */ 
 
#include "arcs.h"
 
/*
pathForArc : Adds an arc (a segment of an oval) fitting inside a rectangle to the path.
 
Parameter Descriptions
context : The CG context to render to.
r : The CG rectangle that defines the arc's boundary..
startAngle : The angle indicating the start of the arc.
arcAngle : The angle indicating the arcÕs extent.
*/
 
void pathForArc(CGContextRef context, CGRect r, int startAngle, int arcAngle)
{
    float start, end;
    CGAffineTransform matrix;
    
    // Save the context's state because we are going to scale it
    CGContextSaveGState(context);
    
    // Create a transform to scale the context so that a radius of 1 maps to the bounds
    // of the rectangle, and transform the origin of the context to the center of
    // the bounding rectangle.
    matrix = CGAffineTransformMake(r.size.width/2, 0,
                                   0, r.size.height/2,
                                   r.origin.x + r.size.width/2,
                                   r.origin.y + r.size.height/2);
                                   
    // Apply the transform to the context
    CGContextConcatCTM(context, matrix);
        
    // Calculate the start and ending angles
    if (arcAngle > 0) {
        start = (90 - startAngle - arcAngle) * M_PI / 180;
        end = (90 - startAngle) * M_PI / 180;
    } else {
        start = (90 - startAngle) * M_PI / 180;
        end = (90 - startAngle - arcAngle) * M_PI / 180;
    }
    
    // Add the Arc to the path
    CGContextAddArc(context, 0, 0, 1, start, end, false);
    
    // Restore the context's state. This removes the translation and scaling
    // but leaves the path, since the path is not part of the graphics state.
    CGContextRestoreGState(context);
}
 
/*
frameArc : Draws an arc of the oval that fits inside a rectangle.
 
Parameter Descriptions
context : The CG context to render to.
r : The CG rectangle that defines the arc's boundary..
startAngle : The angle indicating the start of the arc.
arcAngle : The angle indicating the arcÕs extent.
*/
 
void frameArc(CGContextRef context, CGRect r, int startAngle, int arcAngle)
{
 
    // Signal the start of a path
    CGContextBeginPath(context);
 
    // Add to the path the arc of the oval that fits inside the rectangle.
    pathForArc(context,r,startAngle,arcAngle);
    
    // Stroke the path
    CGContextStrokePath(context);
}
 
/*
paintArc : Paints a wedge of the oval that fits inside a rectangle.
 
Parameter Descriptions
context : The CG context to render to.
r : The CG rectangle that defines the arc's boundary..
startAngle : The angle indicating the start of the arc.
arcAngle : The angle indicating the arcÕs extent.
*/
 
void paintArc(CGContextRef context, CGRect r, int startAngle, int arcAngle)
{
    float start, end;
    
    // Signal the start of a path
    CGContextBeginPath(context);
    
    // Set the start of the path to the arcs focal point
    CGContextMoveToPoint(context, r.origin.x + r.size.width/2, r.origin.y + r.size.height/2);
    
    // Add to the path the arc of the oval that fits inside the rectangle.
    pathForArc(context,r,startAngle,arcAngle);
 
    // Complete the path closing the arc at the focal point
    CGContextClosePath(context);
    
    // Fill the path
    CGContextFillPath(context);
}