[英]OpenGL with GLUT - black screen
我想收到四個三角形的小動畫。 我寫了幾個版本的代碼,但這些版本都不起作用。 結果我有一個空白的黑屏。 我的代碼:
#define GLUT_DISABLE_ATEXIT_HACK
#define TIMERSECS 20
#include <windows.h>
#include <GL/glut.h>
#include <GL/gl.h>
#include <GL/GL.H>
#include <stdlib.h>
float arc = 0.0f;
void draw_traingle(float x0, float y0, float x1, float y1, float x2, float y2) {
glColor4f(0.0f, 0.0f, 1.0f, 1.0f); //Blue
glVertex2f(x0, y0);
glVertex2f(x1, y1);
glVertex2f(x2, y2);
}
void draw(void) {
glLoadIdentity();
glClear(GL_COLOR_BUFFER_BIT);
glRotatef(arc, 1.0f,0.0f,0.0f);
glBegin(GL_POLYGON);
float center_x = 300.0f;
float center_y = 300.0f;
float up_x = center_x;
float up_y = 250.0f;
float down_x = center_x;
float down_y = 350.0f;
float right_x = 350.0f;
float right_y = center_y;
float left_x = 250.0f;
float left_y = center_y;
glPushMatrix();
draw_traingle(up_x, up_y, right_x, right_y, center_x, center_y);
draw_traingle(right_x, right_y, down_x, down_y, center_x, center_y);
draw_traingle(down_x, down_y, left_x, left_y, center_x, center_y);
draw_traingle(left_x, left_y, up_x, up_y, center_x, center_y);
glPopMatrix();
glEnd();
glFlush();
glutSwapBuffers();
}
void handleKeypress(unsigned char key, int x, int y) {
switch (key) {
case 27:
exit(0);
}
}
void init(void) {
glClearColor(0.0, 0.0, 0.0, 0.0);
glViewport(0, 0, 600, 600);
glMatrixMode(GL_PROJECTION);
glLoadIdentity(); //=1
gluOrtho2D(0.0, 600.0, 0.0, 600.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity(); //=1
}
void update(int value) {
arc += 2.0f;
if (arc > 360.f) {
arc -= 360;
}
glutPostRedisplay();
glutTimerFunc(TIMERSECS, update, 0);
}
int main(int argc, char** argv) {
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); //single buffer and RGBA
glutInitWindowSize(600, 600);
glutInitWindowPosition(100, 100);
glutCreateWindow("Window");
init();
glutDisplayFunc(draw);
glutTimerFunc(TIMERSECS, update, 0);
glutKeyboardFunc(handleKeypress);
glutMainLoop();
return 0;
}
我想創建一個動畫,其中我從 traingles 構建的矩形將每隔一段時間旋轉 2 度。 我想像時鍾一樣旋轉它。 我知道問題不及時(不小),而是在 glRotatef 中 - 我不知道應該采用什么參數才能給我適當的效果。
提前致謝! :)
#include <GL/glut.h>
#include <GL/gl.h>
#include <stdlib.h>
//#define TIMERSECS 200 prefer not to use preprocessor macros
//instead you can use:
static const int TIMERSECS = 200;
float arc = 0.0f;
void draw_traingle(float x0, float y0, float x1, float y1, float x2, float y2) {
glBegin(GL_POLYGON);
glColor4f(0.0f, 0.0f, 1.0f, 1.0f); //Blue
glVertex2f(x0, y0);
glVertex2f(x1, y1);
glVertex2f(x2, y2);
glEnd();
}
void draw(void) {
glClear(GL_COLOR_BUFFER_BIT);
glTranslatef(300, 300, 0);
glRotatef(arc, 0.0f,0.0f,1.0f);
glTranslatef(-300, -300, 0);
float center_x = 300.0f;
float center_y = 300.0f;
float up_x = center_x;
float up_y = 250.0f;
float down_x = center_x;
float down_y = 350.0f;
float right_x = 350.0f;
float right_y = center_y;
float left_x = 250.0f;
float left_y = center_y;
draw_traingle(up_x, up_y, right_x, right_y, center_x, center_y);
draw_traingle(right_x, right_y, down_x, down_y, center_x, center_y);
draw_traingle(down_x, down_y, left_x, left_y, center_x, center_y);
draw_traingle(left_x, left_y, up_x, up_y, center_x, center_y);
glutSwapBuffers();
}
void handleKeypress(unsigned char key, int x, int y) {
switch (key) {
case 27:
exit(0);
}
}
void init() {
glClearColor(0.0, 0.0, 0.0, 0.0);
glViewport(0, 0, 600, 600);
glMatrixMode(GL_PROJECTION);
glLoadIdentity(); //=1
gluOrtho2D(0.0, 600.0, 0.0, 600.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity(); //=1
}
void update(int value) {
arc += 2.0f;
if (arc > 360.f) {
arc -= 360;
}
glutPostRedisplay();
glutTimerFunc(200, update, 1);
}
int main(int argc, char** argv) {
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA); //single buffer and RGBA
glutInitWindowSize(600, 600);
glutCreateWindow("Window");
init();
glutDisplayFunc(draw);
glutTimerFunc(TIMERSECS, update, 1);
glutKeyboardFunc(handleKeypress);
glutMainLoop();
return 0;
}
旋轉始終相對於您使用的坐標系。 變換總是以相反的順序應用。 當我們使用 rotatef 函數旋轉一個對象時,它總是相對於坐標系的中心。 所以首先我們需要將它翻譯到中心,這是由 translatef(-300,-300,0) 完成的。 現在對象位於中心。 然后我們使用 rotatef 將對象旋轉到 x、y 或 z 軸。 然后我們再次將對象平移到變換之前的位置。 最后,我們以相反的順序編寫函數。 你已准備好出發 :)
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