[英]function to draw a straight line in c
I'm trying to create a function to draw a straight line by reading two points from the user, (x1,y1) where the line begins and (x2,y2) where it ends.我试图创建一个函数来通过从用户那里读取两个点来绘制一条直线,(x1,y1) 是线的起点,(x2,y2) 是它的终点。 here's my function:这是我的功能:
void line(struct pixels* screen)
{
float X, Y;
int i, j, x1, y1, x2, y2, mX, mY;
scanf("%d%d%d%d", &x1, &y1, &x2, &y2);
if ((x1 >= 0 && x1 <= screen->width) && (y1 >= 0 && y1 <= screen->height) && (x2 >= 0 && x2 <= screen->width) && (y2 >= 0 && y2 <= screen->height))
{
X = (x2 - x1);
Y = (y2 - y1);
if (X < 0)
mX = X*(-1);
else
mX = X;
if (Y < 0)
mY = Y*(-1);
else
mY = Y;
if( mX>mY )
{
if (X > 0)
{
for (i = 0; i < X; i++)
{
j = (int)(((i*Y) / X) + 0.5);
screen->pixel[x1 + i][y1 + j] = '*';
}
}
else
{
for (i = 0; i > X; i--)
{
j = (int)(((i*Y) / X) + 0.5);
screen->pixel[x1 + i][y1 + j] = '*';
}
}
}
else
{
if (Y > 0)
{
for (j = 0; j < Y; j++)
{
i = (int)(((j*X) / Y) + 0.5);
screen->pixel[x1 + i][y1 + j] = '*';
}
}
else
{
for (j = 0; j > Y; j--)
{
i = (int)(((j*X) / Y) + 0.5);
screen->pixel[x1 + i][y1 + j] = '*';
}
}
}
}
else
printf("ERROR: coordinates exceed the screen limits\n");
}
the problem is : when the user enters for example line from (1,1) to (10,10) the code works perfectly, but when it's from (10,10) to (1,1) it doesn't work!问题是:当用户输入例如从 (1,1) 到 (10,10) 的代码时,代码运行良好,但是当它从 (10,10) 到 (1,1) 时,它不起作用!
Google Bresenham's Line Drawing Algorithm.谷歌 Bresenham 的画线算法。 There is a fantastic tutorial/explanation of how do to this kind of thing at How OpenGL works: software renderer in 500 lines of code .在OpenGL 的工作原理:500 行代码中的软件渲染器中,有一个关于如何处理此类事情的精彩教程/解释。 Your specific question is brought up in the article.文章中提出了您的具体问题。 Highly recommended.强烈推荐。
Here is his C++ implementation:这是他的 C++ 实现:
void line(int x0, int y0, int x1, int y1, TGAImage &image, TGAColor color) {
bool steep = false;
if (std::abs(x0-x1)<std::abs(y0-y1)) {
std::swap(x0, y0);
std::swap(x1, y1);
steep = true;
}
if (x0>x1) {
std::swap(x0, x1);
std::swap(y0, y1);
}
int dx = x1-x0;
int dy = y1-y0;
float derror = std::abs(dy/float(dx));
float error = 0;
int y = y0;
for (int x=x0; x<=x1; x++) {
if (steep) {
image.set(y, x, color);
} else {
image.set(x, y, color);
}
error += derror;
if (error>.5) {
y += (y1>y0?1:-1);
error -= 1.;
}
}
}
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