Ref: OpenGL Programming Guide
(The Red Book)

Part 1

Introduction



Geometry
Viewing
Light & Material
Fall 2009 revised
Part 2



Display List
Alpha Channel
Polygon Offset
Part 3


Image
Texture Mapping
Part 4

FrameBuffers

Selection & Feedback
2

Pixels, Bitmaps, and Images

A bitmap is a rectangular array of 0s and 1s that serves as a drawing mask for a rectangular portion of the window
Specification:


Specified, in hex codes, in one dimensional array, row by row, starting from lower-left corner
Width need not be multiples of 8
Fall 2009 revised 4

glBitmap (w, h, xbo, ybo, xbi, ybi, bitmapPtr)
 xbo, ybo: origin
 xbi, ybi: increment CRP after display glBitmap(10, 12, 0, 0, 11, 0, bitmapPtr)
Fall 2009 revised
Fonts: series of bitmaps as display list
5

Note: You can't rotate bitmap fonts because the bitmap is always drawn aligned to the framebuffer axes.
x and y
Use glColor* to set
GL_CURRENT_RASTER_COLOR
Fall 2009 revised 6

OpenGL maintains world coordinate raster position , a 3D-position in
Modified by:

 glRasterPos()

 specify the object coordinates (as in glVertex); transformed by
MODELVIEW & PROJECTION, passed to the clipping stage.
If the position is not culled, raster position is updated; otherwise, it is not valid.
glBitmap() glGetFloatv(GL_CURRENT_RASTER_POSITION, fptr) to obtain the CRP glGetBooleanv
(GL_CURRENT_RASTER_POSITION_VALID, &boolvar) to test validity of CRP
Fall 2009 revised 7

drawf.c
Fall 2009 revised 8

This format is called xwindow bitmap, with xbm extension
Bitmaps can be created by the GIMP
(GNU Image Manipulation Program)
Or, seek format converters
Fall 2009 revised 9

A simple Tk Program; require Tcl/Tk installed
Get tcltk for Windows from
ActiveTcl
Note that xbm and the opengl xbitmap format is slightly different (
details
)
Fall 2009 revised 11

Fall 2009 revised 12

glReadPixels()

Reading pixel data from framebuffer to processor memory.
glDrawPixels()

Writing pixel data from processor memory to framebuffer glCopyPixels()

Copying pixel data within the framebuffer
Fall 2009 revised 13

glReadPixels (x, y, w, h, F, T, ptr)

 x,y: window coordinate
F: pixel format


T: is data type ptr: pointer to image memory glDrawPixels (w, h, F, T, ptr)

Draw to current raster position glCopyPixels (x, y, w, h, buffer)


Buffer: GL_COLOR | GL_DEPTH | GL_STENCIL
Equivalent to: Read then Draw
Fall 2009 revised 14

Note that there's no need for a format or data parameter for glCopyPixels(), since the data is never copied into processor memory.
The read source buffer and the destination buffer of glCopyPixels() are specified by
glReadBuffer() and glDrawBuffer() respectively

Default:
 single-buffer: GL_FRONT
 Double-buffered: GL_BACK
Fall 2009 revised 15

GREY SCALE
GREY SCALE with alpha
Fall 2009 revised 16

Fall 2009 revised 17

255:
0xFF
See also image.c for CopyPixels
Fall 2009 revised 18

Copy the lower left corner to the CRP (where the mouse is)
For single-buffer version, only GL_FRONT is involved
While motion is in action, display is not called
Double-buffer version: [from the API doc] glutSwapBuffers promotes the contents of the back buffer to become the contents of the front buffer. The contents of the back buffer then become undefined. Reality is … two have same content
Fall 2009 revised 19

Enlarge/shrink images
Use negative factors for reflected images
Fall 2009 revised 20

simple TGA utility in gluit.rar
only load and save uncompressed greyscale, RGB or RGBA mode.
images in
Info in TGA header:
 image type [unsigned char]





1 - colour map image
2 - RGB(A) uncompressed
3 - greyscale uncompressed
9 - greyscale RLE (compressed)
10 - RGB(A) RLE (compressed)
 pixel depth [unsigned char]
 8 – greyscale | 24 – RGB | 32 - RGBA
Fall 2009 revised 21

Offline; Local copy at webhd2:game-lib
Fall 2009 revised 22

Fall 2009 revised 23

Fall 2009 revised
Must be freed manually
24

Most graphics formats have image origin at upper/left corner
While OpenGL has the image origin at lower/left corner
Hence, if no correction is done, every image is drawn upside down.
Correction in PNG loader: pngSetStandardOrientation (1);
Fall 2009 revised 25

Fall 2009 revised 26

glPixelStore()


Controlling Pixel-Storage Modes glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
 Packing and unpacking refer to the way that pixel data is written to and read from processor memory.
 tells OpenGL not to skip bytes at the end of a row
Fall 2009 revised 27

PixelStorei(GL_UNPACK_ALIGNMENT, x)
Specifies the alignment requirements for the start of each pixel row in memory. The allowable values are:




1 (byte-alignment),
2 (rows aligned to even-numbered bytes),
4 (word-alignment [default] ), and
8 (rows start on double-word boundaries).
Byte:8-bit
Word:16-bit
Double-word:32-bit
Fall 2009 revised 28

Assuming the RGB image is of size 3x2:
(three bytes per pixel)
In client memory, the start of each row of pixels is … w=3,h=2
Byte aligned (1)
1st row 2nd row
Aligned to even bytes (2); Word aligned (4)
Double word aligned (8)
Fall 2009 revised 29

For RGBA images, it doesn ’ t matter (each pixel has 4 bytes:
RGBARGBA … )
For RGB and luminance images and images with odd width , it should be set to byte-aligned
(data are densely packed) glPixelStorei(GL_UNPACK_ALIGNMENT, 1) glPixelStorei(GL_UNPACK_ALIGNMENT, 4)
Fall 2009 revised 30

A series of fragment operations is applied to pixels as they are drawn into the framebuffer. For optimum performance, disable all fragment operations (depth test, … )
While performing pixel operations, disable other costly states, such as texturing and lighting
It is usually faster to draw a large pixel rectangle than to draw several small ones, since the cost of transferring the pixel data can be amortized ( 分攤 ) over many pixels
Fall 2009 revised 31

Get depth buffer content
 glReadPixels()
Reverse and scale!

Near (white) far (black)
Display it as a luminance image
 glDrawPixels()
Fall 2009 revised 32

Illustrate that CRP is a point in R3
Image displayed is always parallel to projection plane
Fake perspective by zooming with distance to camera
Fall 2009 revised 33

Process sprite image

Add alpha layer
Load png image
Sprite animation
“ feel of depth ”

Back-to-front rendering
 pixelzoom
Fall 2009 revised 34

Texture Mapping (
Introduction )

Specify (create) the texture
Set texture parameters :

Indicate how the texture is to be applied to each pixel
Enable texture mapping
Draw the scene, supplying both texture and geometric coordinates
Works only in RGB mode
Fall 2009 revised 38

glTexImage1D() glTexImage2D() glTexImage3D()
Fall 2009 revised 39

glTexImage2D
(GLenum target, GLint level, GLint components,
GLsizei width, GLsizei height, GLint border, GLenum format, GLenum type, const GLvoid * pixels )
 target
：
GL_TEXTURE_2D


 level ： LOD number (0: base image) components
： number of color components
(1|2|3|4)
Format ： pixel data format


Border: 0 or 1
Width & height


2 m + 2(border bit) w and h can be different
There are new extensions that removes this restriction
Fall 2009 revised 40

In GL version 1.1 or greater, null pointer. pixels may be a
In this case texture memory is allocated to accommodate a texture of width height width
. You can then download and height subtextures to initialize this texture memory.
The image is undefined if the user tries to apply an uninitialized portion of the texture image to a primitive.
Fall 2009 revised 41

glTexEnv{if}{v}(GLenum target,
GLenum pname, TYPEparam);
Setting how textures are to be interpreted:

Target ： GL_TEXTURE_ENV


Pname: GL_TEXTURE_ENV_MODE
Param: modes
(DECAL|REPLACE|MODULATE|BLEND)
Fall 2009 revised 42

GL_REPLACE
GL_MODULATE (default)
GL_DECAL
GL_BLEND
New environment modes:
GL_ADD: C v
= C f
+ C t
GL_COMBINE (ARB, see here )
Fall 2009 revised 43

Color of polygon affects the display of texture
Tree: (r,g,b,a) a cutout
Polygon: (1,0,0)
= 0
Fall 2009 revised 44

Use with: glTexEnvfv
(GL_TEXTURE_ENV,
GL_TEXTURE_ENV_COLOR, colorPtr)
Fall 2009 revised
C c
: texture environment color
45

Appearance solely determined by texture
Tree: (r,g,b,a) a cutout
Polygon: (1,0,0)
= 0
Fall 2009 revised
FOR TEXTURE
CUT-OUTS
46

Tree: (r,g,b,a) a cutout
Polygon: (1,0,0)
= 0
Cp: replace
RGB: DECAL=REPLACE
Fall 2009 revised 47

To show fragment color, use
GL_MODULATE
Apply specular color AFTER texture mapping:
 glLightModeli
(GL_LIGHT_MODEL_COLOR_CONTROL,
GL_SEPARATE_SPECULAR_COLOR);
GL_SEPARATE_SPECULAR_COLOR

See FAQ 21.040
Fall 2009 revised
GL_SINGLE_COLOR
48

Texture coordinate:

Associate texture location (in texture space) with vertices in the polygon glTexCoord2i (s, t); glVertex2i (x, y);
Order cannot be reversed!
[Think of TexCoord as state assignment]
Fall 2009 revised 49

Most quadric primitives have default setting for texture coordinates
To turn on the default setting:
 gluQuadricTexture
(qobj, GL_TRUE)
Fall 2009 revised 50

(1,1)
(0,.75) linear
(1,0)
Polygon (in screen
space) and texture coordinates
Interpolate (s,t) and lookup (r,g,b,a) in the texture map
(0,.75)
Filters nearest
(1,1) rasterization
Fall 2009 revised
Texture map (4x4) (1,0)
51

1
Minification
Magnification
Texels
Pixels
Nature of problem:
Mismatch between texels and pixels
Pixels
Fall 2009 revised 52

Magnification
GL_NEAREST
GL_LINEAR
Nearest: in Manhattan distance to the center of the pixel
Chooses the mipmap that most closely matches the size of the pixel being textured
Minification
GL_NEAREST,
GL_LINEAR,
GL_NEAREST_MIPMAP_NEAREST
GL_LINEAR_MIPMAP_NEAREST
GL_NEAREST_MIPMAP_LINEAR
GL_LINEAR_MIPMAP_LINEAR
Chooses the two mipmaps that most closely match the size of the pixel being textured
Fall 2009 revised 53

GL_LINEAR

Interpolate the texels

More time consuming but more accurate
GL_NEAREST

Snap to the nearest texel
Fall 2009 revised 54

without mipmap
Fall 2009 revised with mipmap
56

Mipmapping was invented by Lance
Williams in 1983 and is described in his paper Pyramidal parametrics .
The most popular method of anti-aliasing for textures
‘Mip’ stands for “ multum in parvo ” = “many things in a small place”
The texture is downsampled to a quarter of the original area.
Level 3 d = the Level Of Detail (LOD)
Level 2
If a pixel covers
2 2

2 2 texels , go to level 2 and get a texel .
2 1

2 1 , level 1
Level 1
2 m-1

2 n-1
Level 0
2 m
m, n

2 n
∈ 
Fall 2009 revised
+
Level 0 Texture 57

glTexParameteri( GL_TEXTURE_2D,
GL_TEXTURE_MIN_FILTER, GL_LINEAR,
GL_NEAREST, GL_LINEAR_MIPMAP_LINEAR,
GL_LINEAR_MIPMAP_NEAREST,
GL_NEAREST_MIPMAP_LINEAR,
GL_NEAREST_MIPMAP_NEAREST );
Remarks:
Mipmap selection is done per pixel
Using not-yet-ready mipmap disables the texture mapping function.
Fall 2009 revised 59

gluBuild2DMipmaps
Storage overhead
1

1
4

1
4
2
  
1
1

1
4

4
3
Fall 2009 revised 60

When the texture coordinates are outside
[0,1] glTexParameteri(GL_TEXTURE_2D,
GL_TEXTURE_WRAP_S,param); glTexParameteri(GL_TEXTURE_2D,
GL_TEXTURE_WRAP_T,param); param: GL_CLAMP|GL_REPEAT
Fall 2009 revised 61

GL_CLAMP
 use the border texel

Diagonal: corner texel
GL_REPEAT
 repeat the texels in
[0,1]
Fall 2009 revised 62

A texture object stores texture data and makes it readily available
You can now control many textures and go back to textures that have been previously loaded into your texture resources
Using texture objects is usually the fastest way to apply textures, resulting in big performance gains
 it is almost always much faster to bind (reuse) an existing texture object than it is to reload a texture image using glTexImage*D()
Fall 2009 revised 63

glGenTextures

Allocate n textures (integer identifiers) glBindTexture

Bind the current texture to specified identifier glDeleteTextures


Free the allocated texture identifiers
Reverse of glGenTextures
Fall 2009 revised 64

Fall 2009 revised checker.c
65

texbind.c
Once created, a named texture may be re-bound to the target of the matching dimensionality as often as needed. It is usually much faster to use glBindTexture to bind an existing named texture to one of the texture targets than it is to reload the texture image using glTexImage1D, glTexImage2D, or
66

Texture properties saved in texture objects:

Minification and magnification filters, wrapping modes, border color and texture priority
When a texture object is bound again, one may edit the contents of the bound texture object. Any commands that change the above properties will change the currently bound texture as well as the current texture state.
Texture environment, texgen, etc. are NOT stored in texture objects
Fall 2009 revised 67

Features

Build mipmap



Load and bind 2D textures
Load image data (image loader)
Handle transparent image (cut-out texture)
Important API
 id = pngBind(filename, mipmap, trans, info, wrapst, minfilter, magfilter)


 pngSetStencil(red, green, blue) pngSetStandardOrientation(1) pngLoad(filename, mipmap, trans, info)
TEXTURE ID IS
RETURNED TO YOU
BY PNG LOADER
Fall 2009 revised 68

Texture coordinates are multiplied by a 4 by 4 matrix before any texture mapping occurs.
Texture animation: using this, you can make the texture slide over the surface, rotate around it, stretch and shrink, …
All matrix operations apply: Push/Pop/Mult/ …
Fall 2009 revised 69

smoke cloud explode water
Fall 2009 revised fire 70

Automatic
ture Coordinate
eration void glTexGen{ifd}{v}(GLenum coord, GLenum
pname, TYPEparam);



Coord: GL_S, GL_T, GL_R, GL_Q
Pname: GL_TEXTURE_GEN_MODE
Type: GL_OBJECT_LINEAR, GL_EYE_LINEAR, or
GL_SPHERE_MAP
Used when the tex coords are too cumbersome to specify, or will be changed with time.
Texture environment, texgen, etc. are NOT stored in texture objects.
Fall 2009 revised 71

Continuous color gradation
(0,1/32,2/32, … , 31/32)
Fall 2009 revised
Discrete white lines
(0,0,0,1,0,0,0,1, … )
72

for a vertex with object coordinates (x o
,y o
,z o
,w o
), generated coordinate = p
1 x o
+ p
2 y o
+ p
3 z o
+ p
4 w
Meaning: when p
1
, p o
2 p
3 coord corresponds to signed distance
, are normalized, this
Similarly, EYE_LINEAR applies to eye coordinates
(0,0,1,0)  (x o
,y o
,z o
,w o
)
Initially, all texture generation functions are set to GL_EYE_LINEAR and are disabled. Both s plane equations are (1, 0, 0, 0), both t plane equations are (0, 1, 0, 0), and all r and q plane equations are (0, 0, 0, 0).
Fall 2009 revised 73

Computing this distance in eye coordinates is a little tricky, since the plane and vertex must first be transformed to eye coordinates. if M is the modelview matrix at the time glTexGenfv( GLX,
GL EYE PLANE, plane ) is called , then the transformed vertex V’ is V’ = M V, let’s call V’ = ( x e
, y e
, z e
, w e
). The plane must also be transformed to get a new plane
A’x +
(
B’y + C’z + D’w = 0 We get ( A’,B’,C’,D’ ) =
A,B,C,D )M − 1 and M is the modelview matrix when glTexGen is invoked . The texture coordinate is then computed as
A’x e
+ B’y e
+ C’z e
+ D’w e
.
Fall 2009 revised 74







 a
 x e y e z w e e






 b

M c






 x o y o z o w o d






, M

 
: a modelview b c d matrix

M

1 tex coord

 a
 b
 c
 d







 x e y e z e w e






Fall 2009 revised 75

What this is
about
…
Extension Wrangler (
GLEW )
Fall 2009 revised 76

Fall 2009 revised 77

(First) ARB-approved extension (1998)
Support up to 32 texture units*
Texture matrix and texgen affects the active texture environment can cascade up to 32 TE ’ s
Note: default blending mode is GL_MODULATE
* glGetIntegerv (GL_MAX_TEXTURE_UNITS, &units);
My platform has only 4! OpenGL 3.1 requires minimum of 16 texture units
Fall 2009 revised 78

OpenGL's multitexture support requires that every texture unit be fully functional and maintain state that is independent of any other texture units.
Each texture unit has its own texture coordinate generation state, texture matrix state, texture enable state, and texture environment state.
However, each texture unit within an OpenGL context shares the same set of texture objects.
Fall 2009 revised 79

Fall 2009 revised 80

When the GL_ARB_multitexture extension is supported, glTexGen set the texture generation parameters for the currently active texture unit, selected with glActiveTexture.

TexUnit0: texture2D;(s,t) given
TexUnit1: texture1D; texGen
81 Fall 2009 revised

From top to bottom
Byte swapping
#define sample_width 16
#define sample_height 10 static char sample_bits[] =
{
0xff,0x00,
0x00,0xff,
0x00,0x00,
0x07,0xe0,
0x00,0x00,
0xf0,0xf8,
0x00,0x00,
0x00,0x00,
0x00,0x00,
0x00,0x00};
Fall 2009 revised 83

Bottom to top & byte swapping
#define sample_width 16
#define sample_height 10 static char sample_bits[] =
{
0x00,0x00,
0x00,0x00,
0x00,0x00,
0x00,0x00,
0x0f,0x1f,
0x00,0x00,
0xe0,0x07,
0x00,0x00,
0x00,0xff,
0xff,0x00};
84

Byte swap: resolved by
 glPixelStorei (GL_UNPACK_LSB_FIRST, 1);
Bottom to top:

Recall width of bitmap need not be multiples of 8, but it is stored in units of unsigned characters


But, the XBM Editor only allows width of multiples of 8 (8,16,24, … )
See the example code on reading it reversely
Fall 2009 revised 85

There seems to no way to make the bitmap larger (than it should be, pixels)
 glPixelZoom won ’ t work!
Therefore, its use is limited
Nevertheless, the color is free to change …
Fall 2009 revised
BACK
86

A way to render realistic picture w/o using too many polygons
Fall 2009 revised
Parallax mapping
87

Texture: a 2D array of color values, each unit is called texel (texture element)
Every texture map has (s,t) coordinates [0,0] to [1,1]
Each vertex in a polygon specifies its texture coordinates (s,t), then map to the given image to determine the corresponding texture
Fall 2009 revised 88

Texture Map
Screen space view
Texture space view
89

Screen space view
Texture Map
Texture space view
OpenGL code
Fall 2009 revised

Fall 2009 revised 91

Fall 2009 revised 92

Fall 2009 revised 93

Fall 2009 revised
BACK
94

The OpenGL standard allows individual vendors to provide additional functionality through extensions as new technology is created. Extensions may introduce new functions and new constants, and may relax or remove restrictions on existing
OpenGL functions.
NV: Each vendor has an alphabetic abbreviation that is used in naming their new functions and constants. For example,
NVIDIA's abbreviation ( NV
GL_NORMAL_MAP_NV .
) is used in defining their proprietary function glCombinerParameterfvNV() and their constant
EXT: It may happen that more than one vendor agrees to implement the same extended functionality. In that case, the abbreviation EXT is used.
ARB: It may further happen that the Architecture Review Board
"blesses" the extension. It then becomes known as a standard extension , and the abbreviation ARB is used.
Fall 2009 revised 95

The second ARB extension was GL_ARB_multitexture , introduced in version 1.2.1. Following the official extension promotion path, multitexturing is no longer an optionally implemented ARB extension, but has been a part of the OpenGL core API since version 1.3.
Before using an extension a program must first determine its availability, and then obtain pointers to any new functions the extension defines. The mechanism for doing this is platformspecific and libraries such as GLEW and GLEE exist to simplify the process.
Specifications for nearly all extensions can be found at the official extension registry
Fall 2009 revised 96

What extension wrangler does:



Your application may find some extensions already available through Microsoft's opengl32.lib. However, depending on your
OpenGL device and device driver, a particular vendor-specific extension may or may not be present at link time.
If it's not present in opengl32.lib, you'll need to obtain the address of the extension's entry points at run time from the device's ICD.
After you obtain the entry point addresses of the extension functions you wish to use, simply call through them as normal function pointers:
FAQ :



How to know which version of OpenGL you are running?
What ’ s the difference among versions?
How to know what extensions are supported?
Ref:

All About OpenGL Extensions
Fall 2009 revised 97

GLEW: OpenGL extension wrangler
Glview: OpenGL extension viewer glewinfo.txt
Fall 2009 revised 98

GL_ARB_multitexture
GL_ARB_texture_cube_map
GL_ARB_texture_env_dot3
ARB
– Extensions officially approved by the OpenGL Architecture Review
Board
EXT
– Extensions agreed upon by multiple
OpenGL vendors
GL_ARB_shadow NV
– NVIDIA Corporation
GL_ARB_vertex_program,
GL_ARB_fragment_program
SGI
– Silicon Graphics
SGIX
– Silicon Graphics (experimental)
GL_ARB_occlusion _query
GL_ARB_texture_non_power_of_two
GL_EXT_texture3D
GL_EXT_framebuffer_object
Fall 2009 revised
BACK
99