opengl - 我有一个关于 opengl glut glutStrokeCharacter 的问题，代码不起作用？

Question

我在 ubuntu 上写了一个 opengl 代码。我想在屏幕上绘制文本，但 output() 函数似乎不起作用。你能告诉我为什么吗？

http://pyopengl.sourceforge.net/documentation/manual/glutStrokeCharacter.3GLUT.html

void output(GLfloat x, GLfloat y, char *text)
{
    char *p;

    glPushMatrix();
    glTranslatef(x, y, 0);
    for (p = text; *p; p++)
    glutStrokeCharacter(GLUT_STROKE_ROMAN, *p);
    glPopMatrix();
}

void myDraw(void)
{
    glClear(GL_COLOR_BUFFER_BIT);

    glColor3f(1.0f,1.0f,0.0f);
    glBegin(GL_POLYGON);
    glVertex2f(-0.8,0.8);
    glVertex2f(-0.2,0.8);
    glVertex2f(-0.2,0.5);
    glVertex2f(-0.8,0.5);
    glEnd();
    glFlush();

    glColor3f(1.0f,0.0f,0.0f);
    output(-0.8,0.8,"hello");     // why not show text

    glFlush();
}

int main(int argc,char ** argv)
{
    printf("init\n");
    glutInit(&argc,argv);
    glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
    glutInitWindowSize(SCALE,SCALE);
    glutInitWindowPosition(100,100);

    glutCreateWindow("MENU");

    glutDisplayFunc(myDraw);

    glutMouseFunc(processMouse);

    glutMainLoop();
    return 0;
}

Answer 1

首先尝试将文本缩小一点:

#include <GL/glut.h>

double aspect_ratio = 0;
void reshape(int w, int h)
{
    aspect_ratio = (double)w / (double)h;
    glViewport(0, 0, w, h);
}

void output(GLfloat x, GLfloat y, char* text)
{
    glPushMatrix();
    glTranslatef(x, y, 0);
    glScalef(1/152.38, 1/152.38, 1/152.38);
    for( char* p = text; *p; p++)
    {
        glutStrokeCharacter(GLUT_STROKE_ROMAN, *p);
    }
    glPopMatrix();
}

void display(void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(-10*aspect_ratio, 10*aspect_ratio, -10, 10, -1, 1);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

    glColor3ub(255,0,0);
    output(0,0,"hello");

    glutSwapBuffers();
}

int main(int argc, char **argv)
{
    glutInit(&argc, argv);
    glutInitDisplayMode(GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE);

    glutInitWindowSize(640,480);
    glutCreateWindow("Text");

    glutDisplayFunc(display);
    glutReshapeFunc(reshape);
    glutMainLoop();
    return 0;
}

如果您阅读您提供的文档，您会发现 GLUT_STROKE_ROMAN默认情况下相当大，大约 152 个单位高。

如果我没记错的话，您所依赖的默认投影和模型 View 矩阵会为您提供一个仅涵盖 (-1,-1) 到 (1,1) 的 View 区域。