Drawing thick line has holes - c++

Question

I've made simple method to draw line with fixed thickness.
Here's my function:
void ColoringScene::drawThickLine(int x1, int y1, int x2, int y2, int r, int g, int b, int a, float wd, bool began, unsigned char* data, unsigned char* areasData){
if(began){
//if just began draw "dot" with filled circle
drawFilledCircle(x1, y1, 1, wd, r, g, b, a, data, areasData);
return;
}
//otherwise calculate angle between two points
int angle = (int)(atan2(-y2 + y1, x2 - x1) * 180 / M_PI);
int a1 = angle - 90;
int a2 = angle + 90;
//calculate a distance between two points
float diff = sqrtf(powf(x1 - x2, 2) + powf(y1 - y2, 2));
if(diff > wd) diff = wd;
//find all points in arc from angle - 90 to angle + 90
for(float _r = a1; _r < a2; _r+=1.0f){
float _x1 = cos(CC_DEGREES_TO_RADIANS(_r)) * wd + x1;
float _y1 = -sin(CC_DEGREES_TO_RADIANS(_r)) * wd + y1;
float _x2 = cos(CC_DEGREES_TO_RADIANS(_r)) * wd + x2;
float _y2 = -sin(CC_DEGREES_TO_RADIANS(_r)) * wd + y2;
//connect point from 2 arcs with line
drawLine(floor(_x1), floor(_y1), floor(_x2), floor(_y2), r, g, b, a, data, areasData);
}
}
it should draw line from (x1, y1) to (x2, y2) with color (r, g, b, a) and thickness wd. I use this method on drawing while moving finger on screen so I've also added extra parameter "began", which says if it's touch began or touch move. data is an array of pixels. areasData does not matter.
But it's not working as expected, here's an example result:
There could be a bit of compression, but you can see 2 dots, which were drawn fine and a curve build from many "thick" lines with holes.
If "wd" is not big enough the problem is not present. I'm almost sure it's some sort of problem with precision.
I tried:
- changing for loop from 0 to 360 (not angle-90, angle+90).
- using round instead of floor
- using sin instead of -sin (y is inverted anyway in my case)
- using _r lower than 1.0 like: 0.05.
And by given fixed thickness (in this example's 60 pixels) there's no way to set parameters like _r increment or angles to not draw without holes.
I decided to write my own function to do this, because other methods I found on web just didn't work as expected (especially with anti-aliasing, which will be perfect solution for me).
Here's drawLine function taken from website: http://willperone.net/Code/codeline.php
void ColoringScene::drawLine(int x1, int y1, int x2, int y2, int r, int g, int b, int a, unsigned char* data, unsigned char* areasData){
int dy = y2 - y1;
int dx = x2 - x1;
int stepx, stepy;
if (dy < 0) { dy = -dy; stepy = -1; } else { stepy = 1; }
if (dx < 0) { dx = -dx; stepx = -1; } else { stepx = 1; }
dy <<= 1; // dy is now 2*dy
dx <<= 1; // dx is now 2*dx
setPixelWithCheckingArea(x1, y1, r, g, b, a, data, areasData);
if (dx > dy)
{
int fraction = dy - (dx >> 1); // same as 2*dy - dx
while (x1 != x2)
{
if (fraction >= 0)
{
y1 += stepy;
fraction -= dx; // same as fraction -= 2*dx
}
x1 += stepx;
fraction += dy; // same as fraction -= 2*dy
setPixelWithCheckingArea(x1, y1, r, g, b, a, data, areasData);
}
} else {
int fraction = dx - (dy >> 1);
while (y1 != y2) {
if (fraction >= 0) {
x1 += stepx;
fraction -= dy;
}
y1 += stepy;
fraction += dx;
setPixelWithCheckingArea(x1, y1, r, g, b, a, data, areasData);
}
}
}