如何画一条斜线
Posted
技术标签:
【中文标题】如何画一条斜线【英文标题】：How do I draw an angled Line 【发布时间】：2021-06-18 14:12:21 【问题描述】：我试着在一个窗口中用 c 画一些线条和形状（没有一个库，它只用一两条线为我做这件事）来学习一点。我已经可以绘制水平和垂直线和矩形。现在，我想画有角度的线。 这是完整的代码：
#include <windows.h>
#include <stdint.h>
typedef uint32_t u32;
int running = 1;
int width = 0;
int height = 0;
int rgb=0;
int pointA[]=100,100;
int pointB[]=200,100;
void* memory;
BITMAPINFO bitmap_info;
//Farben
u32 red = 0xFF0000;
u32 green = 0x00FF00;
u32 blue = 0x0000FF;
u32 black = 0x000000;
u32 white = 0xFFFFFF;
int calculateCord(int x, int y)
int memoryNumber=(height-y+1)*width-(width-x+1);
return memoryNumber;
void setBackground(u32 color)
u32 *pixel = (u32 *)memory;
for (int memoryNumber=0;memoryNumber<width*height;++memoryNumber)
*pixel++=color;
void drawPixel(u32 color,int x,int y)
u32 *pixel = (u32 *)memory;
pixel += calculateCord(x,y);
*pixel=color;
void drawLineHor(u32 color,int x,int y,int lineWidth,int direction)
u32 *pixel=(u32 *)memory;
pixel+=calculateCord(x,y);
for(int a=0;a<lineWidth;a++)
if(direction ==0)
*pixel++=color;
else
*pixel--=color;
void drawLineVert(u32 color,int x,int y,int lineHeight,int direction)
u32 *pixel=(u32 *)memory;
pixel+=calculateCord(x,y);
*pixel=color;
for(int b=0;b<lineHeight;b++)
*pixel=color;
if(direction==0)
pixel-= width;
else
pixel += width;
void drawLineDiagonal(u32 color,int x,int y,int distance,int direction)
u32 *pixel=(u32 *)memory;
pixel+=calculateCord(x,y);
*pixel=color;
for(int a=0;a<distance;a++)
if (direction==0)
*pixel++=color;
pixel -= width;
else
*pixel--=color;
pixel += width;
void drawLineAngle(u32 color,int x,int y,int targetX,int targetY)
u32 *pixel=(u32 *)memory;
pixel += calculateCord(x,y);
*pixel=color;
int difX=targetX-x+1;
int difY=targetY-y+1;
float ratioX= difX/difY;
if(ratioX>=1)
for (int b=0;b<difY;b++)
for(int a=0;a<=ratioX;a++)
*pixel++=color;
*pixel=color;
pixel -= width;
void drawRect(u32 color,int x,int y,int rectWidth,int rectHeight)
u32 *pixel=(u32 *)memory;
pixel+=calculateCord(x,y);
*pixel=color;
for (int a=0;a<rectWidth;a++)
*pixel++=color;
for(int b=0;b<rectHeight;b++)
*pixel=color;
pixel -= width;
for (int a=0;a<rectWidth;a++)
*pixel--=color;
for(int b=0;b<rectHeight;b++)
*pixel=color;
pixel += width;
void fillRect(u32 color,int x,int y,int rectWidth,int rectHeight)
u32 *pixel=(u32 *)memory;
pixel += calculateCord(x,y);
*pixel=color;
for(int b=0;b<rectHeight;b++)
for(int a=0;a<rectWidth;a++)
*pixel++=color;
pixel -= width+rectWidth;
*pixel=color;
LRESULT CALLBACK
WindowProc(HWND window,
UINT message,
WPARAM w_param,
LPARAM l_param)
LRESULT result;
switch(message)
case WM_CLOSE:
running = 0;
printf("Ende");
break;
default:
result = DefWindowProc(window,
message,
w_param,
l_param);
break;
return result;
int WINAPI
wWinMain(HINSTANCE instance,
HINSTANCE prev_instance,
PWSTR cmd_line,
int cmd_show)
WNDCLASS window_class = 0;
wchar_t class_name[] = L"GameWindowClass";
window_class.lpfnWndProc = WindowProc;
window_class.hInstance = instance;
window_class.lpszClassName = class_name;
RegisterClass(&window_class);
HWND window = CreateWindowEx(0,
class_name,
L"Fenster",
WS_OVERLAPPEDWINDOW|WS_VISIBLE,
CW_USEDEFAULT,
CW_USEDEFAULT,
CW_USEDEFAULT,
CW_USEDEFAULT,
0,
0,
instance,
0);
RECT rect;
GetClientRect(window, &rect);
width = rect.right - rect.left;
height = rect.bottom - rect.top;
memory = VirtualAlloc(0,
width * height * 4,
MEM_RESERVE|MEM_COMMIT,
PAGE_READWRITE);
setBackground(black);
drawLineAngled(red,100,100,140,150);
drawPixel(blue,140,150);
drawPixel(green,100,100);
bitmap_info.bmiHeader.biSize = sizeof(bitmap_info.bmiHeader);
bitmap_info.bmiHeader.biWidth = width;
bitmap_info.bmiHeader.biHeight = height;
bitmap_info.bmiHeader.biPlanes = 1;
bitmap_info.bmiHeader.biBitCount = 32;
bitmap_info.bmiHeader.biCompression = BI_RGB;
HDC hdc = GetDC(window);
while(running)
MSG message;
while(PeekMessage(&message, window, 0, 0, PM_REMOVE))
TranslateMessage(&message);
DispatchMessage(&message);
StretchDIBits(hdc,
0,
0,
width,
height,
0,
0,
width,
height,
memory,
&bitmap_info,
DIB_RGB_COLORS,
SRCCOPY);
return 0;
这只是斜线的一部分：
void drawLineAngled(u32 color,int x,int y,int targetX,int targetY)
u32 *pixel=(u32 *)memory;
pixel += calculateCord(x,y);
*pixel=color;
int difX=targetX-x+1;
int difY=targetY-y+1;
float ratioX= difX/difY;
if(ratioX>=1)
for (int b=0;b<difY;b++)
for(int a=0;a<=ratioX;a++)
*pixel++=color;
*pixel=color;
pixel -= width;
当我执行它时，它会画一条有角度的线，但不是重点。这条线在目标点右侧结束一点像素。 我知道代码不是最漂亮的，还有一些地方需要改进，但我想先集中精力。（对不起我的英语）
（编辑） 现在我得到了这个工作正常的代码
void drawAngledLine(u32 color,int originX,int originY,int targetX,int targetY)
int swap=0;
if(originX > targetX || originY > targetY)
int swapX=originX;
originX=targetX;
targetX=swapX;
int swapY=originY;
originY=targetY;
targetY=swapY;
swap=1;
const float m= (float)(targetY-originY)/ (float)(targetX-originX);
const float b= originY-m*(float)originX;
if(m<=1)
for(int x=originX;x<targetX;x++)
float y=m*(float)x+b;
y+=0.5;
drawPixel(color,x,(int)y);
else
const float w=(float)(targetX-originX)/(float)(targetY-originY);
const float v=originX-w*(float)originY;
for(int y=originY;y<targetY;y++)
float x=w*(float)y+v;
x+=0.5;
drawPixel(color,(int)x,y);
if(swap=0)
drawPixel(green,originX,originY);
drawPixel(blue,targetX,targetY);
else
drawPixel(green,targetX,targetY);
drawPixel(blue,targetX,targetY);
【问题讨论】：
“没有库”是否排除了 Windows GDI(+)？ (docs.microsoft.com/en-us/windows/win32/gdi/windows-gdi) 是的，没关系 【参考方案1】：您对下一行for(int a=0;a<=ratioX;a++)中的比率部分的余数有疑问
虽然ratioX 是一个浮点数，但循环将一直工作到数字的整数部分。 ratioX - (int)ratioX 的差异所剩无几。
解决方法与我们解决闰年问题的方法相同。我们累积一年中额外的 6 小时，每 4 年增加一天。同理，你需要把这个差值累加起来，每次累加器经过 1 时增加一个额外的像素（并从累加器中减去 1）。
这会给您留下最后一个像素的问题。有时，即使有所有补偿，您的线也会短一个像素。因此，您可以明确设置targetX,targetY 上的最后一个像素。
以下是基于上述代码的示例：
void drawLineAngled(u32 color,int x,int y,int targetX,int targetY)
u32 *pixel=(u32 *)memory;
pixel += calculateCord(x,y);
*pixel=color;
int difX=targetX-x+1;
int difY=targetY-y+1;
float ratioX= difX/difY;
const float remainderConst=ratioX-(int)ratioX;
float remainder=0;
if(ratioX>=1)
for (int b=0;b<difY;b++)
for(int a=0;a<=ratioX;a++)
*pixel++=color;
// Add the pixel fraction that we had skipped in the loop
remainder+=remainderConst;
// If the skipped fractions accumulate to 1 or more, add a pixel
if (remainder >= 1)
*pixel++=color;
reminder--;
*pixel=color;
pixel -= width;
【讨论】：
所以我把代码改成这样：float ratioX= difX/difY; const float remainderConst=ratioX-(int)ratioX; float remainder=remainderConst; for(int b=0;b<=difY;b++) for(int a=0;a<(int)ratioX;a++) *pixel++=color; remainder += remainderConst; if(remainder>=(float)1) *pixel++=color; remainder--; pixel -= width; 但是这条线大部分时间都是短的，缺少大约 10 到 20 个像素以上是关于如何画一条斜线的主要内容，如果未能解决你的问题，请参考以下文章