CODEWITHSUNDEEP
c++opengl
Ripspace
Ripspace

Reputation: 551

How to make leg movements, OpenGL?

When I try to make leg movements around a pivot point (top of leg), what happens instead is that the legs starts revolving around the wrong point, when I just want the legs to swing back and forth.

How do I fix this problem?

This is my code.

glPushMatrix();

    glTranslatef(x+0.0f, y+6.0f, z-1.5f);
    glRotatef(walk, 1.0f,0.0f,0.0f);
    glBegin(GL_QUADS);
        glTexCoord2f(0.5f,0.0f); glVertex3f(x-1.0f, y-6.0f, z-3.0f);
        glTexCoord2f(1.0f,0.0f); glVertex3f(x-1.0f, y-6.0f, z-0.5f);
        glTexCoord2f(1.0f,0.5f); glVertex3f(x-1.0f, y-18.0f, z-0.5f);
        glTexCoord2f(0.5f,0.5f); glVertex3f(x-1.0f, y-18.0f, z-3.0f);

        glTexCoord2f(0.5f,0.0f); glVertex3f(x+1.0f, y-6.0f, z-3.0f);
        glTexCoord2f(1.0f,0.0f); glVertex3f(x+1.0f, y-6.0f, z-0.5f);
        glTexCoord2f(1.0f,0.5f); glVertex3f(x+1.0f, y-18.0f, z-0.5f);
        glTexCoord2f(0.5f,0.5f); glVertex3f(x+1.0f, y-18.0f, z-3.0f);

        glTexCoord2f(0.5f,0.0f); glVertex3f(x-1.0f, y-6.0f, z-3.0f);
        glTexCoord2f(1.0f,0.0f); glVertex3f(x+1.0f, y-6.0f, z-3.0f);
        glTexCoord2f(1.0f,0.5f); glVertex3f(x+1.0f, y-18.0f, z-3.0f);
        glTexCoord2f(0.5f,0.5f); glVertex3f(x-1.0f, y-18.0f, z-3.0f);

        glTexCoord2f(0.5f,0.0f); glVertex3f(x-1.0f, y-6.0f, z-0.5f);
        glTexCoord2f(1.0f,0.0f); glVertex3f(x+1.0f, y-6.0f, z-0.5f);
        glTexCoord2f(1.0f,0.5f); glVertex3f(x+1.0f, y-18.0f, z-0.5f);
        glTexCoord2f(0.5f,0.5f); glVertex3f(x-1.0f, y-18.0f, z-0.5f);
glEnd();
glPopMatrix();
glPushMatrix();
    glTranslatef(x+0.0f, y+6.0f, z+1.5f);
    glRotatef(-walk, 0.0f,0.0f,1.0f);
    glBegin(GL_QUADS);
        glTexCoord2f(0.5f,0.0f); glVertex3f(x-1.0f, y-6.0f, z+3.0f);
        glTexCoord2f(1.0f,0.0f); glVertex3f(x-1.0f, y-6.0f, z+0.5f);
        glTexCoord2f(1.0f,0.5f); glVertex3f(x-1.0f, y-18.0f, z+0.5f);
        glTexCoord2f(0.5f,0.5f); glVertex3f(x-1.0f, y-18.0f, z+3.0f);

        glTexCoord2f(0.5f,0.0f); glVertex3f(x+1.0f, y-6.0f, z+3.0f);
        glTexCoord2f(1.0f,0.0f); glVertex3f(x+1.0f, y-6.0f, z+0.5f);
        glTexCoord2f(1.0f,0.5f); glVertex3f(x+1.0f, y-18.0f, z+0.5f);
        glTexCoord2f(0.5f,0.5f); glVertex3f(x+1.0f, y-18.0f, z+3.0f);

        glTexCoord2f(0.5f,0.0f); glVertex3f(x-1.0f, y-6.0f, z+3.0f);
        glTexCoord2f(1.0f,0.0f); glVertex3f(x+1.0f, y-6.0f, z+3.0f);
        glTexCoord2f(1.0f,0.5f); glVertex3f(x+1.0f, y-18.0f, z+3.0f);
        glTexCoord2f(0.5f,0.5f); glVertex3f(x-1.0f, y-18.0f, z+3.0f);

        glTexCoord2f(0.5f,0.0f); glVertex3f(x-1.0f, y-6.0f, z+0.5f);
        glTexCoord2f(1.0f,0.0f); glVertex3f(x+1.0f, y-6.0f, z+0.5f);
        glTexCoord2f(1.0f,0.5f); glVertex3f(x+1.0f, y-18.0f, z+0.5f);
        glTexCoord2f(0.5f,0.5f); glVertex3f(x-1.0f, y-18.0f, z+0.5f);
glEnd();

glPopMatrix();

Upvotes: 1

Views: 838

Answers (1)

Spook
Spook

Reputation: 25927

All OpenGL rotations are done around the point (0, 0, 0). So if you want to rotate a vertex around specific point (rx, ry, rz), you have to do the following transformations:

Translate(-rx, -ry, -rz);
Rotate(alpha, beta, gamma);
Translate(rx, ry, rz);

Upvotes: 1

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