OpenGL entry program (3)

1 o'clock:

void TestPoint()
{
    // The size of the point defaults to one pixel, and the size of a point can be set by the following function 
    glPointSize( 50.0f );

    glBegin(GL_POINTS);
    glVertex2f(0, 0);
    glVertex2f(0.5f, 0.5f);

    glEnd();
}

2. Line:

void TestLine()
{
    // Set the width of the line 
    glLineWidth( 500.0f );

    glBegin(GL_LINES);

    glVertex2f(0, 0);
    glVertex2f(0.5f, 0.5f);

    glEnd();
}

3. Dotted line:

// Draw a dotted line 
void TestLineStiple()
{
    // Enable dotted line mode, use glDisable(GL_LINE_STIPPLE) to turn off dotted line mode 
    glEnable(GL_LINE_STIPPLE);

    // Set the width of the line 
    glLineWidth( 500.0f );

    // Set the style of the dotted line
     // Parameter 1: the number of points to be drawn
     // Parameter 2: It is a sequence of 1 and 0 with a length of 16, starting from the lowest bit, if it is 1, the straight line The factor points that should be drawn next will be drawn as real; if it is 0, the factor points that should be drawn next on the line will be drawn as virtual. 
    glLineStipple( 2 , 0x0F0F );

    glBegin(GL_LINES);

    glVertex2f(0, 0);
    glVertex2f(0.5f, 0.5f);

    glEnd();

4. Polygon:

　　1> The two sides of the polygon and how to draw it:

　　　　The polygon has two faces, and each face can be set to a different drawing mode: fill (the default drawing mode), only draw edge outlines, and only draw vertices.

　　　　glPolygonMode(GL_FRONT, GL_FILL); // set front as fill mode

　　　　glPolygonMode(GL_BACK, GL_LINE); // Set the back side as the edge drawing method

　　　　glPolygonMode(GL_FRONT_AND_BACK, GL_POINT); // Set both sides to be vertex drawing

　　2>General convention, counterclockwise is positive, clockwise is negative,

　　　　The concepts of "heads" and "tails" can be swapped with the glFrontFace function.

　　　　glFrontFace(GL_CCW); // Set the CCW direction to "front", CCW is CounterClockWise, counterclockwise

　　　　glFrontFace(GL_CW); // Set the CW direction to "Front", CW is ClockWise, clockwise

void TestPolygon()
{
    // glPolygonMode(GL_FRONT, GL_FILL);             // Set the front to fill mode

    // glPolygonMode(GL_BACK, GL_LINE);              // Set the reverse side as the edge drawing method

    // glPolygonMode(GL_FRONT_AND_BACK, GL_POINT); // Set both sides to be vertex drawing 

    glPolygonMode(GL_FRONT, GL_FILL); // Set front to fill mode 

    glPolygonMode(GL_BACK, GL_LINE);    // Set back to line mode 

    glFrontFace(GL_CCW) ;                // Set the counterclockwise direction to the front 

    glBegin(GL_POLYGON);                // Draw a square counterclockwise, at the bottom left 

    glVertex2f( - 0.5f , - 0.5f );

    glVertex2f(0.0f, -0.5f);

    glVertex2f(0.0f, 0.0f);

    glVertex2f(-0.5f, 0.0f);

    glEnd();

    glBegin(GL_POLYGON);                // Draw a square clockwise at the top right 

    glVertex2f( 0.0f , 0.0f );

    glVertex2f(0.0f, 0.5f);

    glVertex2f(0.5f, 0.5f);

    glVertex2f(0.5f, 0.0f);

    glEnd();

    glFlush();
}

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　　3> Cull polygons:

　　　　glEnable(GL_CULL_FACE) enables culling

　　　 glDisable(GL_CULL_FACE) disable culling

　　　　The parameters of glCullFace can be GL_FRONT, GL_BACK, GL_FRONT_AND_BACK, which means to remove the front, back, and front and back polygons respectively.

　　　　Note: The culling function only affects polygons, not points and lines. For example, with glCullFace(GL_FRONT_AND_BACK), all polygons will be culled, so only points and lines are visible.

OpenGL entry program (3)

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