CODEWITHSUNDEEP
c++opengl
hello
hello

Reputation: 29

openGL gl_Polygon mix color issue

I want to draw two rectangle one on left and one on right with 2 different colors, but after I draw with two GL_Polygon. the image turn out to be this, can anyone help me out? Thank You.

{
    GLfloat rectangleB[5][3]={{10,0,0},{10,30,0},{5,30,0},{1,30,0},{1,0,0}};
    GLfloat rectangleW[5][3]={{0,0,0},{0,30,0},{-5,30,0},{-10,30,0},{-10,0,0}};
    GLfloat rectangleY[5][3]={{8,2,0},{5,28,0},{0,28,0},{-8,28,0},{-8,2,0}};

    void draw_Rectangle(void){

    glBegin(GL_POLYGON);
    for(int i=0;i<5;i++){
        glVertex3fv(rectangleB[i]);
        glColor3f(0.0, 0.0, 1.0);
    }
    glEnd();

    glBegin(GL_POLYGON);
    for(int i=0;i<5;i++){
        glVertex3fv(rectangleW[i]);
        glColor3f(1.0, 1.0, 1.0);
    }
    glEnd();


    glFlush();
}

this is output image

this is the image I want

Upvotes: 0

Views: 337

Answers (1)

Rabbid76
Rabbid76

Reputation: 210878

First of all note, that drawing by glBegin/glEnd sequences is deprecated since several years. Read about Fixed Function Pipeline and see Vertex Specification and Shader for a state of the art way of rendering.

Anyway, glVertex is used to specifies the next vertex coordinate within a glBegin/glEnd sequence.
When glVertex is called, then the current color attribute (glColor) is associated with the vertex coordinate.

This means you have to set the color before you specify the vertex coordinate. Swap glColor3f and glVertex3fv to solve your issue:

glBegin(GL_POLYGON);
for(int i=0;i<5;i++){
    glColor3f(0.0, 0.0, 1.0);
    glVertex3fv(rectangleB[i]);
}
glEnd();

glBegin(GL_POLYGON);
for(int i=0;i<5;i++){
    glColor3f(1.0, 1.0, 1.0);
    glVertex3fv(rectangleW[i]);
}
glEnd();

Upvotes: 2

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