Tutorial Exercise 8 Experiencing with an OpenGL Program
About OpenGL: OpenGL, originally developed by Silicon
Graphics Incorporated (SGI) for their graphics workstations,
lets applications create high-quality color images
independent of windowing systems, operating systems, and
hardware. OpenGL's main purpose is to render two- and
three-dimensional objects into a frame buffer.
On the right is a source code (painting.cpp) of a Visual C++
program which renders a rotating cube using OpenGL.
In previous exercises, you have experienced with some
Visual C++ painting programs. You should be already
familiar with the format of this source code.
CS3162 Introduction to Computer Graphics
Helena Wong, 2001
Download the Visual C++ program from the course web
page for this tutorial. [www.cs.cityu.edu.hk/~helena]
2.
Compile and run this program.
3.
Change the value of gDepthTest (]) to false and rerun the program. What is the difference?
4.
5.
6.
Try to understand the remaining part of this source code.
(Hints: in this code of OpenGL function calls, the coloring
in r,g,b are specified in the range of 0 – 1.0, not 0-255).
You may ask your instructor for anything which you can’t
understand.
Imagine the geometry of the viewing system. Draw it on
a paper. (Hints: you can get the relevant dimensions
from the variables gFieldYOfVew, gZNear, and gZFar.
(v)
Imagine the geometry of the cube in the modeling
coordinate system, ie. According to the code in the
function body: glBegin .. glEnd .., draw the cube with the
axes on a paper, mark which corner is specified with v1,
v2, etc., (Hints: The z-axis is pointing towards you, ie.
Out of the paper).
7. Follow the first page of the handout Simple
Programming with OpenGL, modify this program
as the sample code.
Compile and run the
program.
8. Try some other auxiliary library functions.
glColor3f(0.0, 1.0, 1.0); //v5
glVertex3f(1.0, 1.0, -1.0);
//Initialization settings:
int gNumberOfPicturesPerCycle=20; //no. pictures to be painted in each animation cycle
int gMilliSecondsPerPicture=100;
//time duration for each picture, in milliseconds
COLORREF gBackgroundColor=RGB(0,0,0); //background color: whiteness or blackness are best
int gWidthOfView=400;
//width(in pixels) of the view
int gHeightOfView=300;
//height(in pixels) of the view
float gFieldYOfView=45.0;
float gZNear=3.0;
float gZFar=7.0;
//The field of view, in degrees, in y-direction ------ (v)
//Distance from viewer to the near clipping plane
//Distance from viewer to the far clipping plane
bool gDepthTest=true;
//Enable depth buffer
Tasks:
1.
glVertex3f(1.0, -1.0, 1.0);
// Painting.cpp : implementation file
..
glColor3f(0.0, 1.0, 0.0); //v6
glVertex3f(1.0, -1.0, -1.0);
glColor3f(0.0, 0.0, 1.0); //v7
glVertex3f(-1.0, 1.0, -1.0);
glColor3f(0.0, 0.0, 0.0); //v8
glVertex3f(-1.0, -1.0, -1.0);
glColor3f(1.0, 0.0, 1.0); //v9
glVertex3f(-1.0, 1.0, 1.0);
----- (])
GLfloat gObjectRotationX = 1.0; //degree of rotation(x) of the object in next picture
GLfloat gObjectRotationY = 10.0; //degree of rotation(y) of the object in next picture
GLfloat gObjectRotationZ = 5.0; //degree of rotation(z) of the object in next picture
glColor3f(1.0, 0.0, 0.0); //v10
glVertex3f(-1.0, -1.0, 1.0);
glEnd();
void DoPainting(CDC *pDC,int WhichCallInCurrentCycle)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); //clear with background color
glBegin(GL_QUADS); //draws a quadrilateral
glColor3f(1.0, 0.0, 1.0); //v11
glVertex3f(-1.0, 1.0, 1.0);
glPushMatrix();
glTranslatef(0.0, 0.0, -5.5);
//define a translation
glRotatef(gObjectRotationX, 1.0, 0.0, 0.0); //define a rotation transformation
glRotatef(gObjectRotationY, 0.0, 1.0, 0.0); // with rotation angle and vector
glRotatef(gObjectRotationZ, 0.0, 0.0, 1.0); // of rotation (eg. 1,0,0 = x-axis)
glColor3f(1.0, 1.0, 1.0); //v12
glVertex3f(1.0, 1.0, 1.0);
glColor3f(0.0, 1.0, 1.0); //v13
glVertex3f(1.0, 1.0, -1.0);
gObjectRotationX += 1.0; //prepare for bigger rotation in next picture
gObjectRotationY += 10.0;
gObjectRotationZ += 5.0;
glColor3f(0.0, 0.0, 1.0); //v14
glVertex3f(-1.0, 1.0, -1.0);
glEnd();
glBegin(GL_QUAD_STRIP);
//Draws a connected group of 4 quadrilaterals: q1,q2,q3,q4.
//The vertices are coded in a specific order such that:
//v1,v2,v3,v4 => q1
//v3,v4,v5,v6 => q2
//...
glBegin(GL_QUADS); //draws a quadrilateral
glColor3f(0.5f, 0.5f, 0.5f);
//v15
glVertex3f(-1.0, -1.0, 1.0);
glColor3f(1.0, 0.0, 1.0); //v1
glVertex3f(-1.0, 1.0, 1.0);
glColor3f(1.0, 0.0, 0.0); //v2
glVertex3f(-1.0, -1.0, 1.0);
//v16
glColor3f(0.5f, 0.5f, 0.5f);
glVertex3f(1.0, -1.0, -1.0);
//v17
glColor3f(0.0, 0.0, 0.0);
glVertex3f(-1.0, -1.0, -1.0);
glEnd();
glColor3f(1.0, 1.0, 1.0); //v3
glVertex3f(1.0, 1.0, 1.0);
glColor3f(1.0, 1.0, 0.0); //v4
glColor3f(0.5f, 0.5f, 0.5f);
glVertex3f(1.0, -1.0, 1.0);
glPopMatrix();
}
//v18