Digital Elevation Model. The following are two DEM objects: the left one was rendered with a GLW widget and the right one was rendered with a glw image displayed with a canvas widget. The attached source code highlights a architecture of a molular GUI implementation for scriptive OpenGL rendering with both a GLW widget and a glw image. It shows how to use a Tcl command, glload, to load an image file into a data array. It also shows how to use Tcl commands glexSolidDem and glexWireDem to render a DEM data set in solid and wire modes respectively.
#
A DEM of Grand Canyon rendered
with a GLW widget
A DEM of Grand Canyon rendered
with a glw image displayed
in a canvas widget
# Copyright(c) 1999-2001, Chengye Mao, email: chengye.geo@yahoo.com
#
# dem - To render a 3D digital elevation model (DEM) with a GLW
# widget/image. The DEM data set is a subset of Grand
# Canyon DEM downloaded from USGS's website http://www.usgs.gov.
# Key bindings are provided as a simple API for object rotation,
# translation, zoom in/out of the 3D rendering.
#
# Two entries, dem.create and demcanv.create are provided to
# render the DEM view in a GLW widget or a canvas-hosted glw
# image respectively.
#
# The commands glexSolidDem and glexWireDem are used to calculate
# normals and colors for each vertex in triangle fans defined by
# 3x3 vertex subarrays tiled over the DEM grid. These two commands
# are Tcl commands written in "C". A vertex's normal is defined
# at a plane calculated from four neighboring vertices including
# itself with a least-square-error method. Colors are interpolated
# with blue for the minimum elevation, green for the middle and red
# for the maximum.
#
# Many script lines look like "C" codes required for the same
# rendering except for the key bindings which change the
# parameters of the rendering states and are much simpler in
# Tcl scripts.
#
# Variables of a GLW widget/image can be created with
# commands such as GLint, GLfloat, GLdouble and etc. Variables
# created by these commands have a scope defined by the command
# glw current pathname, which returns the pathname of the
# previous GLW widget/image. The created variables are valid
# during the lifetime of a GLW widget/image unless they are
# deleted with the command gldel. Variables associated with a GLW
# widget/image are freed when the GLW widget/image is
# destroyed or deleted.
#
# A command glload is used to read a DEM image into a variable
# dem. glload can be used to read a binary data stream of
# specified data type into a GLW variable. When an image file
# of black/white or RGB is loaded with glload, the image's rows
# and columns need to be specified separately.
#
# See the glw document for details of glw commands.
#
# Key bindings:
# w display the view in a wire grid
# W display the view in a solid surface
# s z scale decreases
# S z scale increases
# z zoom out the view
# Z zoom in the view
# f field of view decreases
# F field of view increases
# left view moves left
# right view moves right
# up view moves up
# down view moves down
# Q/q stop or start rotation
#
# Binding of mouse motion with the left-button pressed:
# view rotation
#
# Procedures:
# dem.init - initialize
# dem.gen - generate DEM in a OpenGL list
# dem.reshape - configurate a GLW widget
# dem.display - display a GLW widget
# dem.button - handle mouse button
# dem.motion - handle mouse motion
# dem.keypress - handle key press
# dem.rotate - rotate the DEM object by z
# dem.create - entry to ceatte the rendering widget
#
# Procedures to wrap a GLW image into a hosting widget:
# dem.img - create a GLW image for rendering
# dem.img.config - configurate a GLW image with its hosting widget
# dem.img.keypress - handle key press in a hosting widget
# dem.img.bind - binding a hosting widget to dem proccedures
# demcanv.create - entry to create a canvas-hosted GLW image
#
proc dem.init w {
global gimgHome
set old [glw current $w]
glClearColor 0 0 0 0
glload dem [file join $gimgHome tm canyon.lan]
GL_UNSIGNED_BYTE 128
GLint rows 160
GLint cols 184
GLfloat ambient_light {0.2 0.2 0.2 1.0}
GLfloat source_light {0.8 0.8 0.8 1.0}
GLfloat light_pos {1 1 0 1}
GLfloat anglex -70
GLfloat anglez 193
GLfloat fov 32
GLfloat x0 0
GLfloat y0 -0.1
GLfloat z0 -1.4
GLfloat sz 0.2
GLint moving
GLint startx
GLint starty
GLuint listid
# Set up simple lighting model
glEnable GL_LIGHTING
glLightModel GL_LIGHT_MODEL_AMBIENT ambient_light
glLight GL_LIGHT0 GL_DIFFUSE source_light
glLight GL_LIGHT0 GL_POSITION light_pos
glEnable GL_LIGHT0
glEnable GL_AUTO_NORMAL
glEnable GL_NORMALIZE
# Enable material properties for lighting
glEnable GL_COLOR_MATERIAL
glColorMaterial GL_FRONT GL_AMBIENT_AND_DIFFUSE
glset listid [glGenLists 1]
dem.gen $w
glw current $old
}
proc dem.gen {w {mode Solid}} {
_busyIcon
set old [glw current $w]
glNewList listid GL_COMPILE
glex${mode}Dem cols rows 1 1 sz dem
glEndList
glw current $old
}
proc dem.reshape {w width height} {
set old [glw current $w]
glViewport 0 0 $width $height
glMatrixMode GL_PROJECTION
glLoadIdentity
gluPerspective fov [expr $width/double($height)]
0.1 20.0
glw current $old
}
proc dem.display w {
set old [glw current $w]
glClear GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT
glColor 1 1 1
glMatrixMode GL_MODELVIEW
glLoadIdentity
glEnable GL_DEPTH_TEST
glDepthFunc GL_LEQUAL
glPushMatrix
glTranslate x0 y0 z0
glRotate anglex 1 0 0
glRotate anglez 0 0 1
glRotate 0 0 1 0
glCallList listid
glPopMatrix
glw draw
glw current $old
}
proc dem.button {w state x y} {
set old [glw current $w]
if {$state == "BUTTON_DOWN"} {
glset moving 1
glset startx $x
glset starty $y
}
if {$state == "BUTTON_UP"} {
glset moving 0
}
glw current $old
}
proc dem.motion {w x y} {
set old [glw current $w]
if {[glv moving]} {
glset anglez [expr [glv
anglez] + 0.5 * ($x - [glv startx])]
glset anglex [expr [glv
anglex] + 0.5 * ($y - [glv starty])]
glset startx $x
glset starty $y
dem.display $w
}
glw current $old
}
proc dem.keypress {w keycode keysym} {
set old [glw current $w]
switch $keysym {
"Escape" { glw delete
$w }
"w"
{ dem.gen $w Wire }
"W"
{ dem.gen $w Solid }
"s"
{ glset sz [expr [glv sz]-0.05]; dem.gen $w }
"S"
{ glset sz [expr [glv sz]+0.05]; dem.gen $w }
"z"
{ glset z0 [expr [glv z0]-0.01] }
"Z"
{ glset z0 [expr [glv z0]+0.01] }
"Left" {
glset x0 [expr [glv x0]-0.01] }
"Right" { glset
x0 [expr [glv x0]+0.01] }
"Up"
{ glset y0 [expr [glv y0]+0.01] }
"Down" {
glset y0 [expr [glv y0]-0.01] }
"f"
{ glset fov [expr [glv fov]-1.0] \
dem.reshape $w [$w cget -width] [$w cget -height]}
"F"
{ glset fov [expr [glv fov]+1.0] \
dem.reshape $w [$w cget -width] [$w cget -height]}
"q"
-
"Q"
{ dem.queue $w }
}
catch {
dem.display $w
glw current $old
update
}
}
proc dem.rotate w {
set old [glw current $w]
glset anglez [expr [glv anglez] + 2.0]
if { [glv anglez] == 360.0 } {
glset anglez 0
}
dem.display $w
glw current $old
}
proc dem.queue w {
set old [glw current $w]
if [catch "glv qid"] {
GLint qid [queue.put
"dem.rotate $w"]
} else {
queue.remove [glv
qid]
gldel qid
}
glw current $old
}
proc dem.create w {
glw $w -width 340 -height 196
dem.init $w
bind $w <Expose>
"dem.display $w"
bind $w <Configure>
"dem.reshape $w %w %h"
bind $w <ButtonPress> "dem.button
$w BUTTON_DOWN %x %y"
bind $w <ButtonRelease> "dem.button $w BUTTON_UP
%x %y"
bind $w <Motion>
"dem.motion $w %x %y"
bind $w <KeyPress>
"dem.keypress $w %k %K"
focus $w
dem.display $w
return $w
}
proc dem.img img {
image create glw $img -width 180 -height 90
dem.init $img
dem.reshape $img 180 90
dem.display $img
return $img
}
proc dem.img.config {w img wwd wht} {
set bd [$w cget -bd]
set width [expr $wwd - 2 * $bd]
set height [expr $wht - 2 * $bd]
$img config -width $width -height $height
dem.reshape $img $width $height
dem.display $img
}
proc dem.img.keypress {w img k K} {
switch $K {
"Escape" {destroy $w}
default {dem.keypress
$img $k $K}
}
}
proc dem.img.bind {w img} {
bind $w <Configure>
"dem.img.config $w $img %w %h"
bind $w <ButtonPress> "dem.button
$img BUTTON_DOWN %x %y"
bind $w <ButtonRelease> "dem.button $img
BUTTON_UP %x %y"
bind $w <Motion>
"dem.motion $img %x %y"
bind $w <KeyPress>
"dem.img.keypress $w $img %k %K"
focus $w
}
proc demcanv.create canv {
canvas $canv -width 320 -height 196
$canv create image 0 0 -image [dem.img dem$canv]
-anchor nw
$canv create text 10 10 -fill red -anchor nw
\
-text "3D View of Grand
Canyon with OpenGL"
dem.img.bind $canv dem$canv
bind $canv <Destroy> "catch {image delete
dem$canv}"
return $canv
}