2005-09-01

About Assignments

• Assignment requirement: Paper copy
• Easier to give comments
• Some drawings(if necessary) will help understand the code
• GLUT in CS machines
• Option 1: Bundle your own pre-built GLUT header file and library
Make sure your Makefile work! Test it in SEL 2260 CS Computer lab.

GLUT = ./glut INC_DIR = ./glut/include LIB_DIR = ./glut/lib INC += -I$(INC_DIR) LIB += -L$(LIB_DIR)

• Option 2: Use i488 installed version
~i488/glut/include

~i488/glut/lib



• `turnin' your homework files
• About how `turnin' and `project' work
• `turnin' manpage
• Homework 1 is now open to submit


turnin -v -c cs488 -p hw1 files

• Feedback and discussions
• Email: ychen@cs.uic.edu
• UIC Blackboard - Discussions
If you cannot get in, please let me know by Email.

OpenGL APIs

• OpenGL command syntax

glVertex2i(10, 24);

glColor3f(12.2, 0.34, -3.2);

GLfloat color_array[] = {0.2, 1.0, 0.7}; glColor3fv(color_array);

• Data types

*Notice: The following table is from `OpenGL Programming Guide (Addison-Wesley Publishing Company)' online version here.

Table 1-1 : Command Suffixes and Argument Data Types

Suffix	Data Type	Typical Corresponding C-Language Type	OpenGL Type Definition
b	8-bit integer	signed char	GLbyte
s	16-bit integer	short	GLshort
i	32-bit integer	long	GLint, GLsizei
f	32-bit floating-point	float	GLfloat, GLclampf
d	64-bit floating-point	double	GLdouble, GLclampd
ub	8-bit unsigned integer	unsigned char	GLubyte, GLboolean
us	16-bit unsigned integer	unsigned short	GLushort
ui	32-bit unsigned integer	unsigned long	GLuint, GLenum, GLbitfield

• OpenGL as a state machine
Like using Photoshop in a really primitive way.

Select color -> select tools(operations) -> draw(describe graphics primitives)

Set and get your current status

glGetDoublev(); glGetIntegerv(); ... glGet* *(See redboot Appendix B for state variables)

Detecting OpenGL Functionality: ... // Check core version: strVersion = glGetString (GL_VERSION); // Verify extension support: strExt = glGetString (GL_EXTENSIONS); // Determine OpenGL limits: glGetIntegerv (GL_MAX_TEXTURE_SIZE, &maxTextureSize); (*From Apple Developer OpenGL tutorial documents)

• Rendering mode
• Immediate mode
• Display lists (Ch7)
Common hardware will make it more efficient
• Drawing geomateic objects
• Clear window
• Select color
glClearColor(R, G, B, A);
• Action
glClear(GLbitfield mask);

The mask:

(*Notice: The following table is from `OpenGL Programming Guide (Addison-Wesley Publishing Company)' online version here.)

Buffer	Name	Reference
Color buffer	GL_COLOR_BUFFER_BIT	Chapter 5
Depth buffer	GL_DEPTH_BUFFER_BIT	Chapter 10
Accumulation buffer	GL_ACCUM_BUFFER_BIT	Chapter 10
Stencil buffer	GL_STENCIL_BUFFER_BIT	Chapter 10

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); v.s. glClear(GL_COLOR_BUFFER_BIT); glClear(GL_DEPTH_BUFFER_BIT);

• Set color
glColor3f(0.0, 1.0, 0.0);

glColor3f(0.1, 0.3, 0.2);

...

• Describe points, lines and polygons
• Points
• Lines
• (Simple) Polygons
• Rectangles
• More? By approximation
Specifying vertices:

Between glBegin(GLenum mode); and glEnd();

Different types:

(*Notice: The following diagram is from `OpenGL Programming Guide (Addison-Wesley Publishing Company)' online version here.)



• Vertics connection ordering: V0, V1, V2, ... , Vn-1
• GL_POINTS
n vertices
• GL_LINES
If n is odd, Vn-1 is ignored.
• GL_LINE_STRIP
n-1 line segments
• GL_LINE_LOOP
Like GL_LINE_STRIP. And V0 and Vn-1 is connected.
• GL_TRIANGLES
(V0, V1, V2), (V3, V4, V5)...
• GL_TRIANGLES_STRIP
(V0, V1, V2), (V2, V1, V3), (V2, V3, V4)...

Index is counter-clockwise.

Make sure the strip will form a surface.

• GL_TRIANGLE_FAN
(V0, V1, V2), (V0, V2, V3), (V0, V3, V4)...

Shared V0.

• GL_QUADS
(V0, V1, V2, V3), (V4, V5, V6, V7)...

Extra 1, 2, or 3 vertices at the end are ignored.

• GL_QUAD_STRIP
(V0, V1, V2, V3), (V2, V3, V5, V4), (V4, V5, V6 V7)...
• GL_POLYGON
The polygon must be convex and and intersect itself, otherwise the result is unpredictable (implementation dependant).

(*Notice: The following diagram is from `OpenGL Programming Guide (Addison-Wesley Publishing Company)' online version here.)

Valid Commands between glBegin() and glEnd()

Command	Purpose of Command	Reference
glVertex*()	set vertex coordinates	Chapter 2
glColor*()	set current color	Chapter 5
glIndex*()	set current color index	Chapter 5
glNormal*()	set normal vector coordinates	Chapter 2
glEvalCoord*()	generate coordinates	Chapter 11
glCallList(), glCallLists()	execute display list(s)	Chapter 4
glTexCoord*()	set texture coordinates	Chapter 9
glEdgeFlag*()	control drawing of edges	Chapter 2
glMaterial*()	set material properties	Chapter 6

• Execute commands
• glFlush();
"just do it"
• glFinsh();
needs ack. for synchronization.
• glutSwapBuffers();
GLUT, double-buffering
• Example code: Draw a circle

#define PI 3.1415926535897; GLint circle_points = 100; glBegin(GL_LINE_LOOP); for (i = 0; i < circle_points; i++) { angle = 2*PI*i/circle_points; glVertex2f(cos(angle), sin(angle)); } glEnd();

• Basic state management
• Enable/Disable
glEnable(GLenum cap);

glDisable(GLenum cap);

GL_BLEND, GL_DEPTH_TEST, GL_FOG, GL_LINE_STIPPLE, GL_LIGHTING

• Query state
• glIsEnabled(GLenum cap);
• glGetBooleanv(GLenum cap, GLboolean *params);
• glGetIntegerv(GLenum cap, GLint *params);
• glGetFloatv(GLenum cap, GLfloat *params);
• glGetDoublev(GLenum cap, GLdouble *params);
• glGetPointerv(GLenum cap, GLvoid **params);

// Determine OpenGL limits: GLint maxTextureSize; glGetIntegerv (GL_MAX_TEXTURE_SIZE, &maxTextureSize);

• Display points, lines, polygons
• Points
• void glPointSize(GLfloat size);
• Query point size range with `GL_ALIAS_POINT_SIZE_RANGE' state variable (with glGetFloatv();)
• Query point size range with `GL_SMOOTH_POINT_SIZE_RANGE' state variable (with glGetFloatv();)
• Lines
• void glLineWidth(GLfloat width);
• Query line width size range with `GL_ALIAS_LINE_WIDTH_RANGE' state variable (with glGetFloatv();)
• Stippled Lines
void glLineStipple(GLint factor, GLushort pattern);

Pattern: 16-bit series of 0s and 1s. Repeat.

glLineStipple(1, 0x3F07); glEnable(GL_LINE_STIPPLE); (ps. 0x3F07 -> 0011111100000111)



-> Example code: See what you can do with GL_LINES and GL_LINE_STRIP

• Polygons
• As points, outlines or solids
Two faces of polygon. Front and back

void glPolygonMode(GLenum face, GLenum mode); ---- face: GL_FRONT_AND_BACK, GL_FRONT, GL_BACK mode: GL_POINT, GL_LINE, GL_FILL Default: Both front and back are GL_FILL ---- glPolygonMode(GL_FRONT, GL_FILL); glPolygonMode(GL_BACK, GL_LINE);

• Reversing and Culling polygon faces
Change polygon's front face from using `counter-clockwise' to `clockwise'.

void glFrontFace(GLenum mode); // GL_CCW, or GL_CW

Culling: tell OpenGL to discard front-facing or back-faceing polygons.

void glEnable(GL_CULL_FACE); // mode could be // GL_FRONT, GL_BACK, GL_FRONT_AND_BACK void glCullFace(GLenum mode);

• Stippling polygons

glEnable(GL_POLYGON_STIPPLE); void glPolygonStipple(const GLubyte *mask); glDisable(GL_POLYGON_STIPPLE); Mask: 32x32 bitmap -> Example code

• Normal vector
• Perpendicular to a surfce
• In OpenGL, vertex or polygon will have normal vector
• Normal vector matters when have lighting enabled.
The orientation the object and light position and orientation will determine how much light the object receives. Especially in three dimension.
• Lighting -> CH5

void glNormal3{bsidf}(TYPE nx, TYPE ny, TYPE nz); void glNormal3P{bsidf}v(const TYPE *v); ---- glBegin(GL_POLYGON); glNormal3fv(n0); glVertex3fv(v0); glNormal3fv(n1); glVertex3fv(v1); glNormal3fv(n2); glVertex3fv(v2); glEnd();

• Normal means directions only. Length is irrelevant.

To get unit normal vector: length = sqrt( x^2 + y^2 + z^2 ); unit_normal = ( nx/length, ny/length, nz/length );

• To have OpenGL automatically normalized normal vector after transformation

Default: both off Reason: Enable hits performance glEnable(GL_NORMALIZE); glEnable(GL_RESCALE_NORMAL); // cheaper

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