[SDL2] Draw and fill a circle

circle.cpp

int
SDL_RenderDrawCircle(SDL_Renderer * renderer, int x, int y, int radius)
{
    int offsetx, offsety, d;
    int status;

    CHECK_RENDERER_MAGIC(renderer, -1);

    offsetx = 0;
    offsety = radius;
    d = radius -1;
    status = 0;

    while (offsety >= offsetx) {
        status += SDL_RenderDrawPoint(renderer, x + offsetx, y + offsety);
        status += SDL_RenderDrawPoint(renderer, x + offsety, y + offsetx);
        status += SDL_RenderDrawPoint(renderer, x - offsetx, y + offsety);
        status += SDL_RenderDrawPoint(renderer, x - offsety, y + offsetx);
        status += SDL_RenderDrawPoint(renderer, x + offsetx, y - offsety);
        status += SDL_RenderDrawPoint(renderer, x + offsety, y - offsetx);
        status += SDL_RenderDrawPoint(renderer, x - offsetx, y - offsety);
        status += SDL_RenderDrawPoint(renderer, x - offsety, y - offsetx);

        if (status < 0) {
            status = -1;
            break;
        }

        if (d >= 2*offsetx) {
            d -= 2*offsetx + 1;
            offsetx +=1;
        }
        else if (d < 2 * (radius - offsety)) {
            d += 2 * offsety - 1;
            offsety -= 1;
        }
        else {
            d += 2 * (offsety - offsetx - 1);
            offsety -= 1;
            offsetx += 1;
        }
    }

    return status;
}


int
SDL_RenderFillCircle(SDL_Renderer * renderer, int x, int y, int radius)
{
    int offsetx, offsety, d;
    int status;

    CHECK_RENDERER_MAGIC(renderer, -1);

    offsetx = 0;
    offsety = radius;
    d = radius -1;
    status = 0;

    while (offsety >= offsetx) {

        status += SDL_RenderDrawLine(renderer, x - offsety, y + offsetx,
                                     x + offsety, y + offsetx);
        status += SDL_RenderDrawLine(renderer, x - offsetx, y + offsety,
                                     x + offsetx, y + offsety);
        status += SDL_RenderDrawLine(renderer, x - offsetx, y - offsety,
                                     x + offsetx, y - offsety);
        status += SDL_RenderDrawLine(renderer, x - offsety, y - offsetx,
                                     x + offsety, y - offsetx);

        if (status < 0) {
            status = -1;
            break;
        }

        if (d >= 2*offsetx) {
            d -= 2*offsetx + 1;
            offsetx +=1;
        }
        else if (d < 2 * (radius - offsety)) {
            d += 2 * offsety - 1;
            offsety -= 1;
        }
        else {
            d += 2 * (offsety - offsetx - 1);
            offsety -= 1;
            offsetx += 1;
        }
    }

    return status;
}

I implemented these two function into SDL_render.c. But I couldn't push my commits in the mercurial repository (^.^').

SDL_RenderDrawCircle is based on the midpoint circle algorithm.
SDL_RenderFillCircle : the idea behind this function can be found here and here

You can remove CHECK_RENDERER_MAGIC, it was used because it was planned to be used in SDL2.

The source code is under the MIT Licence

where did chech_render_magic come from?

where did chech_render_magic come from?

They already mentioned it here. Just comment that line out.

You can remove CHECK_RENDERER_MAGIC, it was used because it was planned to be used in SDL2.

In case you wanna see the source code:
https://github.com/libsdl-org/SDL/blob/228d9ae7915ec2c841605aedfaa627c441626740/src/render/SDL_render.c#L48

where did chech_render_magic come from?

They already mentioned it here. Just comment that line out.

You can remove CHECK_RENDERER_MAGIC, it was used because it was planned to be used in SDL2.

In case you wanna see the source code: https://github.com/libsdl-org/SDL/blob/228d9ae7915ec2c841605aedfaa627c441626740/src/render/SDL_render.c#L48

oh ok, i missed

Thanks. This is really helpful.

Thank you!