c++ - 文字颜色不正确

Question

void text(string str)
{
    for (int i = 0; i < str.length(); i++)
    {
        glColor3f(0.0f, 0.0f, 0.0f);
        glutBitmapCharacter(GLUT_BITMAP_TIMES_ROMAN_24, str[i]);
    }
}

void render(void)
{
    int width  = glutGet(GLUT_WINDOW_WIDTH);
    int height = glutGet(GLUT_WINDOW_HEIGHT);
    if (height == 0) height = 1;
    GLfloat aspect = (GLfloat)width / (GLfloat)height;

    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glEnable(GL_SCISSOR_TEST);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(45.0f, aspect, 0.1f, 100.0f);

    // Top view - top left
    glViewport(0, 0, width/2, height/2);
    glScissor(0, 0, width/2, height/2);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    PilotView(0.0f, 0.0f, -5.0f, 0.0f, 0.0f, 0.0f, 1.0f);
    glRasterPos3f(-0.1f, -0.1f, 4.0f);
    text("Front");
    diode();

    // Corner view - top right
    glViewport(width/2, 0, width/2, height/2);
    glScissor(width/2, 0, width/2, height/2);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    PilotView(0.0f, 0.0f, -5.0f, 0.0f, -90.0f, 0.0f, 1.0f);
    glRasterPos3f(4.0f, -0.1f, 0.1f);
    text("Right");
    diode();

    // Front view - bottom left
    glViewport(0, height/2, width/2, height/2);
    glScissor(0, height/2, width/2, height/2);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    PilotView(0.0f, 0.0f, -5.0f, 90.0f, 0.0f, 0.0f, 1.0f);
    glRasterPos3f(-0.1f, 4.0f, 0.0f);
    text("Top");
    diode();

    // Right view - bottom right
    glViewport(width/2, height/2, width/2, height/2);
    glScissor(width/2, height/2, width/2, height/2);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    PilotView(0.0f, 0.0f, -5.0f, 20.0f, 0.0f, 0.0f, 1.0f);
    glRasterPos3f(-0.1f, 4.0f, 0.0f);
    text("Fro4nt");
    diode();

    glDisable(GL_SCISSOR_TEST);
    glutSwapBuffers();
}

我不确定白色的“正面”和黄色的“顶部”/“右侧”来自哪里(就颜色而言)。他们都应该是黑色的。有谁知道问题出在哪里？

输出如下:

Answer 1

正如所怀疑的那样，这可能会令人震惊，但 glRasterPos (...) 实际上会在您调用该函数时跟踪“当前”颜色。也就是说，在调用 glRasterPos (...) 之前设置的任何颜色都将用作该位置绘图操作的“当前颜色”。几乎可以将其视为光栅化器对 glVertex (...) 的模拟，正如我将在下面解释的那样。

您需要在调用 glRasterPos (...) 之前设置当前颜色，为此您应该完全删除 glColor3f (...) 调用您的 text (...) 函数，或者修改该函数以执行这两项操作 - 设置颜色，然后设置光栅位置，然后绘制文本。

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glRasterPos — specify the raster position for pixel operations :

The current raster position consists of three window coordinates (x, y, z), a clip coordinate value (w), an eye coordinate distance, a valid bit, and associated color data and texture coordinates.