Pattern Flood Fill Algorithm - c

Question

I have implemented a flood fill algorithm that is working correctly for solid color fills. Now I´m working on a pattern fill and decided to add a flag to see how to fill the area ( with a color or with a pattern). However when using the the algorithm with pattern fill gets stuck while painting the area.
This is my original code that works with solid colors:
void floodFillStack(int x, int y, byte newColor, byte oldColor) {
int y1;
if (oldColor == newColor) return;
if (get_pixel(x, y) != oldColor) return;
//draw current scanline from start position to the top
y1 = y;
while (y1 < h && get_pixel(x, y1) == oldColor) {
plot_pixel(x, y1, newColor);
y1++;
}
//draw current scanline from start position to the bottom
y1 = y - 1;
while (y1 >= 0 && get_pixel(x, y1) == oldColor) {
plot_pixel(x, y1, newColor);
y1--;
}
//test for new scanlines to the left
y1 = y;
while (y1 < h && get_pixel(x, y1) == newColor) {
if (x > 0 && get_pixel(x - 1, y1) == oldColor) {
floodFillStack(x - 1, y1, newColor, oldColor);
}
y1++;
}
y1 = y - 1;
while (y1 >= 0 && get_pixel(x, y1) == newColor) {
if (x > 0 && get_pixel(x - 1, y1) == oldColor) {
floodFillStack(x - 1, y1, newColor, oldColor);
}
y1--;
}
//test for new scanlines to the right
y1 = y;
while (y1 < h && get_pixel(x, y1) == newColor) {
if (x < w - 1 && get_pixel(x + 1, y1) == oldColor) {
floodFillStack(x + 1, y1, newColor, oldColor);
}
y1++;
}
y1 = y - 1;
while (y1 >= 0 &&get_pixel(x, y1) == newColor) {
if (x < w - 1 && get_pixel(x + 1, y1) == oldColor) {
floodFillStack(x + 1, y1, newColor, oldColor);
}
y1--;
}
}
And here is with the pattern modification (it still works with solid colors).
int pattern1[6][6] = { {0,1,0,1,0,1},
{1,0,1,0,1,0},
{0,1,0,1,0,1},
{1,0,1,0,1,0},
{0,1,0,1,0,1},
{1,0,1,0,1,0} };
int pattern2[6][6] = { {0,0,1,1,0,0},
{0,1,0,0,1,0},
{1,0,0,0,0,1},
{1,0,0,0,0,1},
{0,1,0,0,1,0},
{0,0,1,1,0,0} };
void floodFillStack(int x, int y, byte newColor, byte oldColor, int pattern_fill) {
int y1;
if (oldColor == newColor) return;
if (get_pixel(x, y) != oldColor) return;
//draw current scanline from start position to the top
y1 = y;
while (y1 < h && get_pixel(x, y1) == oldColor) {
if (pattern_fill == 0) {
if (fill_pattern == 1) {
if (pattern1[x%6][y1%6] == 1) {
plot_pixel(x, y1, newColor);
}
} else {
if (pattern2[x%6][y1%6] == 1) {
plot_pixel(x, y1, newColor);
}
}
} else {
plot_pixel(x, y1, newColor);
}
y1++;
}
//draw current scanline from start position to the bottom
y1 = y - 1;
while (y1 >= 0 && get_pixel(x, y1) == oldColor) {
if (pattern_fill == 0) {
if (fill_pattern == 1) {
if (pattern1[x%6][y1%6] == 1) {
plot_pixel(x, y1, newColor);
}
} else {
if (pattern2[x%6][y1%6] == 1) {
plot_pixel(x, y1, newColor);
}
}
} else {
plot_pixel(x, y1, newColor);
}
y1--;
}
//test for new scanlines to the left
y1 = y;
while (y1 < h && get_pixel(x, y1) == newColor) {
if (x > 0 && get_pixel(x - 1, y1) == oldColor) {
floodFillStack(x - 1, y1, newColor, oldColor, pattern_fill);
}
y1++;
}
y1 = y - 1;
while (y1 >= 0 && get_pixel(x, y1) == newColor) {
if (x > 0 && get_pixel(x - 1, y1) == oldColor) {
floodFillStack(x - 1, y1, newColor, oldColor, pattern_fill);
}
y1--;
}
//test for new scanlines to the right
y1 = y;
while (y1 < h && get_pixel(x, y1) == newColor) {
if (x < w - 1 &&get_pixel(x + 1, y1) == oldColor) {
floodFillStack(x + 1, y1, newColor, oldColor, pattern_fill);
}
y1++;
}
y1 = y - 1;
while (y1 >= 0 && get_pixel(x, y1) == newColor) {
if (x < w - 1 && get_pixel(x + 1, y1) == oldColor) {
floodFillStack(x + 1, y1, newColor, oldColor, pattern_fill);
}
y1--;
}
}
Can anyone help me see the problem?
EDIT:
Thanks to WeatherVane for the suggestion. The algorithm is no longer stuck, but it does not cover the entire area. Here´s a picture:

Answer 1

Your floodfill is likely to misfire if you ignore the 0 values in your pattern masks. Instead of that, always fill with one of two colours (both different from the background).
You will also have to change some of your conditional tests. Instead of
(... == newColor)
you could use
(... != oldColor)
or
(... == newColor1 || ... == newColor2)

Answer 2

When you fill with a solid color, every pixel that starts at oldColor gets changed to newColor. This means that a test of that pixel later in the process won't match against it again.
When you try to fill with a pattern, some of those pixels are going to remain as oldColor. You get stuck in an infinite loop, retesting those same pixels over and over.