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1. Lecture 05: OpenGL 2 (Fixed-Function) COMP 175: Computer Graphics
September 19, 2011
2. Conceptual Graphics Framework
Graphics Library can be Direct3D, Java3D, OpenGL, etc.
It is a software API that controls the functions of a piece of hardware – the graphics card. Remember…
3. In Immediate-Mode Fixed-Function mode, OpenGL acts as a state machine.
What is a state machine?
Every variable is a “global variable”
For example, the current color
You need to keep track of the states… Or query the graphics card if you forget
Which, of course, is slow Graphics Library
4. Pseudo code:
SetState (LineStyle, DASHED);
SetState (LineColor, RED);
DrawLine ( PtStart = (x1,y1), PtEnd = (x2,y2) );
SetState (LineColor, BLUE);
DrawLine ( PtStart = (x2,y2), PtEnd = (x3,y3) );
SetState (LineStyle, SOLID);
DrawLine ( PtStart = (x3,y3), PtEnd = (x4,y4) ); State Variables
5. Pseudo code:
SetState (LineStyle, DASHED);
SetState (LineColor, RED);
DrawLine ( PtStart = (x1,y1), PtEnd = (x2,y2) );
SetState (LineStyle, DASHED);
SetState (LineColor, BLUE);
DrawLine ( PtStart = (x2,y2), PtEnd = (x3,y3) );
SetState (LineStyle, SOLID);
SetState (LineColor, BLUE);
DrawLine ( PtStart = (x3,y3), PtEnd = (x4,y4) ); State Variables
6. What if…?
function DrawDashedTriangle (pt1,pt2,p3) {
SetState( LineStyle, DASHED );
DrawLine( PtStart=pt1, PtStart=p2 );
DrawLine( PtStart=pt2, PtStart=p3 );
DrawLine( PtStart=pt3, PtStart=p1 );
}
What color is the triangle?
Pros:??
Cons:?? State Variables – Pros and Cons
7. What if…?
function DrawDashedTriangle (pt1,pt2,p3) {
SetState( LineStyle, DASHED );
DrawLine( PtStart=pt1, PtStart=p2 );
DrawLine( PtStart=pt2, PtStart=p3 );
DrawLine( PtStart=pt3, PtStart=p1 );
}
What color is the triangle?
Pros: trickle down effect, caller can control the subroutine’s behavior
Cons: the color is undefined! Who set my color?! State Variables – Pros and Cons
8. What’s right and what’s wrong with this?
function DrawTriangle (pt1,pt2,p3,
int origColor, int curColor,
int origStyle, int curStyle ) {
SetState( LineStyle, curStyle );
SetState(LineColor, curColor);
DrawLine( PtStart=pt1, PtStart=p2 );
DrawLine( PtStart=pt2, PtStart=p3 );
DrawLine( PtStart=pt3, PtStart=p1 );
SetState( LineStyle, origStyle );
SetState(LineColor, origColor);
} State Variables – Pros and Cons
9. Bundles and unsets…
function DrawRedDashedTriangle(pt1,pt2,p3){
PushAttributeState();
SetState( LineStyle, DASHED );
SetState( LineColor, RED );
...
PopAttributeState();
}
This eliminates the state variable problem. Still A Pain, but Cleaner…
10. What if I forget to set some state?
DrawLine ( PtStart = (x1,y1), PtEnd = (x2,y2) );
What if I set the wrong state?
SetState(LineStyle, 12345);
DrawLine( PtStart=pt1, PtStart=p2 );
What if I forget the state a variable is in?
Forgetting the State?
11. What if I forget to set some state?
DrawLine ( PtStart = (x1,y1), PtEnd = (x2,y2) );
OpenGL provides some good default values. For example, for color, it’s set to (1,1,1,1) – non transparent white
How do I know if something worked?
SetState(LineStyle, 12345);
DrawLine( PtStart=pt1, PtStart=p2 );
You don’t. Since it’s not clear if some configuration of states will send OpenGL spinning, if you suspect an error from OpenGL, call
Glenum glGetError(void)
What if I forget the state a variable is in?
You should use this sparingly… But you can use
void glGetBooleanv(Glenum paraname, Glboolean* params)
void glGetFixedv(Glenum paraname, Glfixed* params)
void glGetFloatv(Glenum paraname, Glfloat* params)
void glGetIntegerv(Glenum paraname, Glint* params)
Forgetting the State?
12.
What do you think is the best way to deal with the state machine and maintain state variables?
How to access local variables (that correspond to state variables)?
Efficiency considerations?
How do you think the programming with a state machine affects multi-threaded applications? Programming Strategies?
13. How many parameters do you have to pass to render an object?
void render () {
obj1->drawSelf(myMouse, myScreenSize, myTimer, ...);
obj2->drawSelf(myMouse, myScreenSize, myTimer, ...);
obj3->drawSelf(myMouse, myScreenSize, myTimer, ...);
}
How do you enforce that there is only one instance of myMouse, myScreenSize, myTimer in code?
For Example
14. Use global variables
Use mutual references. For example:
Possible Answers?
15. Problems:
Need to guarantee a single instance of the states
Don’t want to pass a billion parameters during the execution of every child object
Don’t want the child to have to call parent->parent->parent->parent->getProperties();
One possible answer is to use Singletons Possible Answers?
16.
What do you think is the best way to deal with the state machine and maintain state variables?
How to access local variables (that correspond to state variables)?
Efficiency considerations?
How do you think the programming with a state machine affects multi-threaded applications? Programming Strategies?
17. Thread A Thread B void drawRedDashedTriangle()
{
pushAttributes();
setColor (RED);
setStyle (DASHED);
drawLine (pt1+d, pt2+d);
drawLine (pt2+d, pt3+d);
drawLine (pt3+d, pt1+d);
d++;
popAttributes();
} void drawBlueSolidTriangle()
{
pushAttributes();
setColor (BLUE);
setStyle (SOLID);
drawLine (pt4-p, pt5-p);
drawLine (pt5-p, pt6-p);
drawLine (pt6-p, pt4-p);
p--;
popAttributes();
}
Multi-Threading and OpenGL
18. Thread A Thread B void drawRedDashedTriangle()
{
mutex.lock();
pushAttributes();
setColor (RED);
setStyle (DASHED);
drawLine (pt1+d, pt2+d);
drawLine (pt2+d, pt3+d);
drawLine (pt3+d, pt1+d);
d++;
popAttributes();
mutex.unlock();
} void drawBlueSolidTriangle()
{
mutex.lock();
pushAttributes();
setColor (BLUE);
setStyle (SOLID);
drawLine (pt4-p, pt5-p);
drawLine (pt5-p, pt6-p);
drawLine (pt6-p, pt4-p);
p--;
popAttributes();
mutex.unlock();
}
Multi-Threading and OpenGL
19.
Questions?
20. Typical OpenGL Application
21. Here we use GLUT, which is a basic GL window implementation that is on all platforms.
Pros: cross-platform, command line, easy to use
Cons: no GUI support (no buttons, menus, etc.) Example
22. int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
glutInitWindowPosition( 50, 50 ); //upper left
glutInitWindowSize( 640, 480 ); // width, height, in pixels
glutCreateWindow( "OpenGL Example" ); // window title
glViewport(
/* lower left corner of the viewport */ 0, 0,
/* width, height of the viewport */ 640, 480 ); //lower left Example OpenGL Application
23.
int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
Example OpenGL Application
24. int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode( GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH );
glutInitWindowPosition( 50, 50 ); //upper left
glutInitWindowSize( 640, 480 ); // width, height, in pixels
glutCreateWindow( "OpenGL Example" ); // window title
glViewport(
/* lower left corner of the viewport */ 0, 0,
/* width, height of the viewport */ 640, 480 ); //lower left Example OpenGL Application
26. int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH );
glutInitWindowPosition( 50, 50 ); //upper left
glutInitWindowSize( 640, 480 ); // width, height, in pixels
glutCreateWindow( "OpenGL Example" ); // window title
glViewport(
/* lower left corner of the viewport */ 0, 0,
/* width, height of the viewport */ 640, 480 ); //lower left
glShadeModel( GL_SMOOTH );
glPolygonMode( GL_FRONT, GL_FILL );
setupLighting();
setupCamera(640, 480);
registerCallBacks();
glutMainLoop();
}
Example OpenGL Application
27. int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH );
glutInitWindowPosition( 50, 50 ); //upper left
glutInitWindowSize( 640, 480 ); // width, height, in pixels
glutCreateWindow( "OpenGL Example" ); // window title
glViewport(
/* lower left corner of the viewport */ 0, 0,
/* width, height of the viewport */ 640, 480 ); //lower left
glShadeModel( GL_SMOOTH );
glPolygonMode( GL_FRONT, GL_FILL );
setupLighting();
setupCamera(640, 480);
registerCallBacks();
glutMainLoop();
}
Example OpenGL Application
28. int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH );
glutInitWindowPosition( 50, 50 ); //upper left
glutInitWindowSize( 640, 480 ); // width, height, in pixels
glutCreateWindow( "OpenGL Example" ); // window title
glViewport(
/* lower left corner of the viewport */ 0, 0,
/* width, height of the viewport */ 640, 480 ); //lower left
glShadeModel( GL_SMOOTH );
glPolygonMode( GL_FRONT, GL_FILL );
setupLighting();
setupCamera(640, 480);
registerCallBacks();
glutMainLoop();
}
Example OpenGL Application
29. int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH );
glutInitWindowPosition( 50, 50 ); //upper left
glutInitWindowSize( 640, 480 ); // width, height, in pixels
glutCreateWindow( "OpenGL Example" ); // window title
glViewport(
/* lower left corner of the viewport */ 0, 0,
/* width, height of the viewport */ 640, 480 ); //lower left
glShadeModel( GL_SMOOTH );
glPolygonMode( GL_FRONT, GL_FILL );
setupLighting();
setupCamera(640, 480);
registerCallBacks();
glutMainLoop();
}
Example OpenGL Application
30. int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH );
glutInitWindowPosition( 50, 50 ); //upper left
glutInitWindowSize( 640, 480 ); // width, height, in pixels
glutCreateWindow( "OpenGL Example" ); // window title
glViewport(
/* lower left corner of the viewport */ 0, 0,
/* width, height of the viewport */ 640, 480 ); //lower left
glShadeModel( GL_SMOOTH );
glPolygonMode( GL_FRONT, GL_FILL );
setupLighting();
setupCamera(640, 480);
registerCallBacks();
glutMainLoop();
}
Example OpenGL Application
31. void myReshape(GLint width, GLint height) {
//called when the window is resized
glViewport(0, 0, width, height);
setupCamera(width, height);
}
void myKeyboard (unsigned car key, int x, int y) {
//called on keyboard event
switch (key) {
case ‘a’:
someGlobalVariable = 1;
:
:
}
} Example OpenGL Application
32. void myMouseClick(int button, int state, int x, int y) {
//called when a mouse click occurs
if (button == GLUT_LEFT_BUTTON) {
if (state == GLUT_DOWN) {
globalVariableMouseDown = true;
}
else {
globalVariableMouseDown = false;
}
}
}
void myMouseMove (int x, int y) {
//called when a mouse move occurs
if (globalVariableMouseDown==true)
{
//dragging occurs
}
}
Example OpenGL Application
33. void display(void) {
//called when the window needs to paint itself
glClear (GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
drawMyStuff();
glutSwapBuffers();
numberOfFrames++;
}
void myIdle (void) {
//called ALL THE TIME!!
DWORD time_now = GetTickCount();
float diff = (float)(time_now-last_check_time)/1000.0;
if (diff > 1.0) {
float frameRate = numberOfFrames / (float)diff;
numberOfFrames = 0;
last_check_time = time_now;
}
glutPostRedisplay();
}
Example OpenGL Application
34. int main( int argc, char** argv ) {
glutInit( &argc, argv ); // Boilerplate initialization
glutInitDisplayMode( GLUT_RGB | GLUT_DEPTH );
glutInitWindowPosition( 50, 50 ); //upper left
glutInitWindowSize( 640, 480 ); // width, height, in pixels
glutCreateWindow( "OpenGL Example" ); // window title
glViewport(
/* lower left corner of the viewport */ 0, 0,
/* width, height of the viewport */ 640, 480 ); //lower left
glShadeModel( GL_SMOOTH );
glPolygonMode( GL_FRONT, GL_FILL );
setupLighting();
setupCamera(640, 480);
registerCallBacks();
glutMainLoop();
}
Example OpenGL Application
35. Typical OpenGL Application
36.
Questions?
37. void drawMyStuff(void) {
glBegin (...);
//glColor3f(1.0f, 1.0f, 1.0f);
//glNormal3f(0.0f, 0.0f, 1.0f);
glVertex3f(1.0f, 1.0f, 1.0f);
glVertex3f(1.0f, 2.0f, 1.0f);
:
:
glEnd();
} Drawing Primitives
38. GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON OpenGL Primitives
39. GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON OpenGL Primitives
40. GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON OpenGL Primitives
41. GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON OpenGL Primitives
42. void glFrontFace (GLenum mode)
mode can be either GL_CW or GL_CCW
GL_CCW is the default
Ordering of Vertices
43. GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON OpenGL Primitives
44. GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON OpenGL Primitives
45. GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON OpenGL Primitives
46. GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON OpenGL Primitives
47. GL_POINTS GL_LINES GL_LINE_STRIP GL_LINE_LOOP GL_TRIANGLES GL_TRIANGLE_STRIP GL_TRIANGLE_FAN GL_QUADS GL_QUAD_STRIP GL_POLYGON OpenGL Primitives
48. glColor3f (1.0, 0.0f, 0.0f);
glBegin(GL_TRIANGLES);
glVertex3f(-1.0f, -0.5f, -4.0f); // A
glVertex3f( 1.0f, -0.5f, -4.0f); // B
glVertex3f( 0.0f, 0.5f, -4.0f); // C
glEnd(); Color Blending
49. glBegin(GL_TRIANGLES);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex3f(-1.0f, -0.5f, -4.0f); // A
glColor3f(0.0f, 1.0f, 0.0f);
glVertex3f( 1.0f, -0.5f, -4.0f); // B
glColor3f(0.0f, 0.0f, 1.0f);
glVertex3f( 0.0f, 0.5f, -4.0f); // C
glEnd(); Color Blending
50. glShadeModel( GL_FLAT );
glBegin(GL_TRIANGLES);
glColor3f(1.0f, 0.0f, 0.0f);
glVertex3f(-1.0f, -0.5f, -4.0f); // A
glColor3f(0.0f, 1.0f, 0.0f);
glVertex3f( 1.0f, -0.5f, -4.0f); // B
glColor3f(0.0f, 0.0f, 1.0f);
glVertex3f( 0.0f, 0.5f, -4.0f); // C
glEnd(); GL Shade Model
51. The direction where the face of the triangle points towards
Unit vector
Or call ( glEnable(GL_NORMALIZE); )
GL Normal
52. These two have the same number of quads…
What is the difference? GL Normal
53. GL Normal
54. glNormal3f(nx, ny, nz);
glBegin(GL_QUADS);
glVertex3f(x1, y1, z1);
glVertex3f(x2, y2, z2);
glVertex3f(x3, y3, z3);
glVertex3f(x4, y4, z4);
glEnd();
GL Normal
55. glBegin(GL_QUADS);
glNormal3f(nx1, ny1, nz1);
glVertex3f(x1, y1, z1);
glNormal3f(nx2, ny2, nz2);
glVertex3f(x2, y2, z2);
glNormal3f(nx3, ny3, nz3);
glVertex3f(x3, y3, z3);
glNormal3f(nx4, ny4, nz4);
glVertex3f(x4, y4, z4);
glEnd();
GL Normal
56.
Questions?
