Question

Using Cocos2d to draw a thicker circle:

glLineWidth(20);
ccDrawCircle(self.ripplePosition, _radius, 0, 50, NO);

But this is what shows up(notice how it looks like it’s created from 4 different segments):

https://i.stack.imgur.com/jYW4s.png

I tried increasing the number of segments to larger values but the result is the same.

Is this a bug in Cocos2D? Any ideas on how to achieve a “perfect” circle?

Here is the implementation of ccDrawCircle from cocos2d 2.0rc2:

void ccDrawCircle( CGPoint center, float r, float a, NSUInteger segs, BOOL drawLineToCenter)
{
lazy_init();

int additionalSegment = 1;
if (drawLineToCenter)
    additionalSegment++;

const float coef = 2.0f * (float)M_PI/segs;

GLfloat *vertices = calloc( sizeof(GLfloat)*2*(segs+2), 1);
if( ! vertices )
    return;

for(NSUInteger i = 0;i <= segs; i++) {
    float rads = i*coef;
    GLfloat j = r * cosf(rads + a) + center.x;
    GLfloat k = r * sinf(rads + a) + center.y;

    vertices[i*2] = j;
    vertices[i*2+1] = k;
}
vertices[(segs+1)*2] = center.x;
vertices[(segs+1)*2+1] = center.y;

[shader_ use];
[shader_ setUniformForModelViewProjectionMatrix];    
[shader_ setUniformLocation:colorLocation_ with4fv:(GLfloat*) &color_.r count:1];

ccGLEnableVertexAttribs( kCCVertexAttribFlag_Position );

glVertexAttribPointer(kCCVertexAttrib_Position, 2, GL_FLOAT, GL_FALSE, 0, vertices);
glDrawArrays(GL_LINE_STRIP, 0, (GLsizei) segs+additionalSegment);

free( vertices );

CC_INCREMENT_GL_DRAWS(1);
}

Answer 1

I went with a slightly modified version of ccDrawCircle and it works pretty well (performs a lot better than using and resizing a sprite):

void ccDrawDonut( CGPoint center, float r1, float r2, NSUInteger segs)
{
    lazy_init();

    const float coef = 2.0f * (float)M_PI/segs;

    GLfloat *vertices = calloc( sizeof(GLfloat)*4*segs+4, 1);
    if( ! vertices )
        return;

    for(NSUInteger i = 0;i <= segs; i++) {
        float rads = i*coef;
        GLfloat j1 = r1 * cosf(rads) + center.x;
        GLfloat k1 = r1 * sinf(rads) + center.y;
        vertices[i*4] = j1;
        vertices[i*4+1] = k1;

        rads+= coef/2;
        GLfloat j2 = r2 * cosf(rads) + center.x;
        GLfloat k2 = r2 * sinf(rads) + center.y;

        vertices[i*4+2] = j2;
        vertices[i*4+3] = k2;
    }

    [shader_ use];
    [shader_ setUniformForModelViewProjectionMatrix];
    [shader_ setUniformLocation:colorLocation_ with4fv:(GLfloat*) &color_.r count:1];

    ccGLEnableVertexAttribs( kCCVertexAttribFlag_Position );

    glVertexAttribPointer(kCCVertexAttrib_Position, 2, GL_FLOAT, GL_FALSE, 0, vertices);
    glDrawArrays(GL_TRIANGLE_STRIP, 0, (GLsizei) 2*segs+2);

    free( vertices );

    CC_INCREMENT_GL_DRAWS(1);
}