用OpenGL实现折线和矩形的橡皮筋绘制技术（可完全脱离鼠标）

发表于 更新于 分类于 ，

这学期开始学计算机图形学基础，课后有个习题让用OpenGL实现折线和矩形的橡皮筋绘制技术，只要求了用右键菜单实现功能的选择。老师嫌有些简单，就说要加上教材上基于键盘实现的代码，可教材上的代码还是要先把鼠标移到一个点上，再用按键确定这个点，这样配合着使用很别扭。我想既然用键盘了，不如直接写个可以完全由键盘控制绘图过程的代码吧。

正好现在我想学下Python，就决定拿这道题开始练手。代码虽然很简单，但写的过程中，一边要学Python的语法，一边又要查OpenGL的库函数，还是挺费精力的。这算是我第一次用Python写代码，结果还算满意，写个博客纪念下吧。

程序用鼠标完成绘图就不用说了。键盘方面  A、D、W、X 用于移动窗口内的点，P用于选定某一点，L、 R、 C 分别为菜单各功能的快捷键，用于选择画折线、画矩形或清除图形。所有按键不区分大小写。为了使程序使用方便，键盘和鼠标没做什么限制，既可以分别使用，也可以结合使用。代码如下：

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268

#!/usr/bin/python
from OpenGL.GL import *
from OpenGL.GLU import *
from OpenGL.GLUT import *

iMode=1
winWidth = 800; winHeight = 600
num = 0; a = [0]*100; b = [0]*100
w1 = 200; h1 = 500; w2 = 200; h2 = 500
iPointNum = 0; x1 = 200; y1 = 500; x2 = 200; y2 = 500

def ChangeSize(w, h):
    global winWidth, winHeight
    winWidth = w
    winHeight = h
    glViewport(0, 0, w, h)
    glMatrixMode(GL_PROJECTION)
    glLoadIdentity()
    gluOrtho2D(0.0, winWidth, 0.0, winHeight)

def ProcessMenu(value):
    global iMode
    iMode = value
    glutPostRedisplay()

def DrawPoint(x , y):
    glClear(GL_COLOR_BUFFER_BIT)
    glPointSize(1.5)
    glBegin(GL_POINTS)
    glVertex2i(x, y)
    glEnd()
    glutSwapBuffers()


def Draw():
    glClearColor(0.0, 0.0, 0.0, 0.0)
    glClear(GL_COLOR_BUFFER_BIT)
    glColor3f(1.0, 0.0, 0.0)

    global num, iMode, w1, h1, w2, h2, x1, x2, y1, y2, iPointNum, a, b
    #Line
    if iMode == 1:
        glBegin(GL_LINE_STRIP)
        for i in range(0, num):
            glVertex2i(a[i], b[i])
        glEnd()

        if num > 0:
            glBegin(GL_LINES)
            glVertex2i(w1, h1)
            glVertex2i(w2, h2)
            glEnd()

    #Rectangle
    elif iMode == 2 and iPointNum > 0:
        glBegin(GL_LINES)
        glVertex2i(x1, y1)
        glVertex2i(x2, y1)
        glEnd()

        glBegin(GL_LINES)
        glVertex2i(x1, y1)
        glVertex2i(x1, y2)
        glEnd()

        glBegin(GL_LINES)
        glVertex2i(x2, y1)
        glVertex2i(x2, y2)
        glEnd()

        glBegin(GL_LINES)
        glVertex2i(x1, y2)
        glVertex2i(x2, y2)
        glEnd()

    elif iMode == 3:
        num = 0
        iPointNum = 0
        w1 = w2 = x1 = x2 = 200
        h1 = h2 = y1 = y2 = 500

    glutSwapBuffers()

def MousePlot(button, action, xMouse, yMouse):
    global num, iMode, winHeight, w1, h1, w2, h2, x1, x2, y1, y2, iPointNum, a, b
    if iMode == 1:
    	if button == GLUT_LEFT_BUTTON and action == GLUT_DOWN:
	    if num == 0:
		w1 = xMouse
		h1 = winHeight - yMouse
		a[num] = w1; b[num] = h1
		num += 1
	    else:
                w2 = xMouse
                h2 = winHeight - yMouse
		a[num] = w2; b[num] = h2
		num += 1
		w1 = w2; h1 = h2
		glutPostRedisplay()
	elif button == GLUT_RIGHT_BUTTON and action == GLUT_DOWN:
	    num = 0
	    glutPostRedisplay()

    elif iMode == 2:
	if button == GLUT_LEFT_BUTTON and action == GLUT_DOWN:
	    if iPointNum == 0 or iPointNum == 2:
		iPointNum = 1
		x1 = xMouse
		y1 = winHeight - yMouse
            else:
	        iPointNum = 2
	        x2 = xMouse
	        y2 = winHeight - yMouse
	        glutPostRedisplay()
	elif button == GLUT_RIGHT_BUTTON and action == GLUT_DOWN:
	    iPointNum = 0

def Key(key, xMouse, yMouse):
    global num, iMode, winWidth, winHeight, w1, h1, w2, h2, x1, x2, y1, y2, iPointNum
    #python has no switch statements
    if key == 'l' or key == 'L':
        iMode = 1
        glutPostRedisplay()

    elif key == 'r' or key == 'R':
        iMode = 2
        glutPostRedisplay()

    elif key == 'c' or key =='C':
        iMode = 3
        glutPostRedisplay()

    elif key == 'p' or key == 'P':
        if iMode == 1:
            if num == 0:
                a[num] = w1; b[num] = h1
                num += 1
            else:
                a[num] = w2; b[num] = h2
                num += 1
                w1 = w2; h1 = h2
                glutPostRedisplay()

        elif iMode == 2:
            if iPointNum == 0 or iPointNum == 2:
                iPointNum = 1
            else:
                iPointNum = 2
                glRecti(x1, y1, x2, y2)
                glutSwapBuffers()

    elif key == 'a' or key == 'A':
        if iMode == 1:
            if num == 0:
                if w1 >= 5:
                    w1 -= 5
                DrawPoint(w1, h1)
            else:
                if w2 >= 5:
                    w2 -= 5
                    glutPostRedisplay()

        elif iMode == 2:
            if iPointNum == 0 or iPointNum == 2:
                if x1 >= 5:
                    x1 -= 5
                DrawPoint(x1, y1)
            else:
                if x2 >= 5:
                    x2 -= 5
                glutPostRedisplay()
    elif  key == 'd' or key == 'D':
        if iMode == 1:
            if num == 0:
                if w1 <= winWidth - 5:
                    w1 += 5
                DrawPoint(w1, h1)
            else:
                if w2 <= winWidth - 5:
                    w2 += 5
                    glutPostRedisplay()

        elif iMode == 2:
            if iPointNum == 0 or iPointNum == 2:
                if x1 <= winWidth - 5:
                    x1 += 5
                DrawPoint(x1, y1)
            else:
                if x2 <= winWidth - 5:
                    x2 += 5
                glutPostRedisplay()

    elif  key == 'w' or key == 'W':
        if iMode == 1:
            if num == 0:
                if h1 <= winHeight - 5:
                    h1 += 5
                DrawPoint(w1, h1)
            else:
                if h2 <= winHeight - 5:
                    h2 += 5
                    glutPostRedisplay()

        elif iMode == 2:
            if iPointNum == 0 or iPointNum == 2:
                if y1 <= winHeight - 5:
                    y1 += 5
                DrawPoint(x1, y1)
            else:
                if y2 <= winHeight - 5:
                    y2 += 5
                glutPostRedisplay()

    elif  key == 'x' or key == 'X':
        if iMode == 1:
            if num == 0:
                if h1 >= 5:
                    h1 -= 5
                DrawPoint(w1, h1)
            else:
                if h2 >= 5:
                    h2 -= 5
                    glutPostRedisplay()

        elif iMode == 2:
            if iPointNum == 0 or iPointNum == 2:
                if y1 >= 5:
                    y1 -= 5
                DrawPoint(x1, y1)
            else:
                if y2 >= 5:
                    y2 -= 5
                glutPostRedisplay()

def PassiveMouseMove(xMouse, yMouse):
    global iMode, num, w2, h2, x1, y1, x2, y2, winHeight, iPointNum
    if iMode == 1:
	if num > 0:
	    w2 = xMouse
	    h2 = winHeight - yMouse
	    glutPostRedisplay()

    elif iMode == 2:
	if iPointNum == 1:
	    x2 = xMouse
	    y2 = winHeight - yMouse
	    glutPostRedisplay()
        elif iPointNum == 2:
            glRecti(x1, y1, x2, y2)
            glutSwapBuffers()

glutInit()
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGBA)
glutInitWindowSize(800, 600)
glutInitWindowPosition(100, 100)
glutCreateWindow("3-11 Line and Rectangle")
glutCreateMenu(ProcessMenu)
glutAddMenuEntry("Line(L)", 1)
glutAddMenuEntry("Rectangle(R)", 2)
glutAddMenuEntry("Clear(C)", 3)
glutAttachMenu(GLUT_RIGHT_BUTTON)
glutDisplayFunc(Draw)
glutReshapeFunc(ChangeSize)
glutKeyboardFunc(Key)
glutMouseFunc(MousePlot)
glutPassiveMotionFunc(PassiveMouseMove)
glutMainLoop()