Demo ogl_alpha_blending_texture
Demo 2 of 19 in category CodeSampler
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#-----------------------------------------------------------------------------
# Name: ogl_alpha_blending_texture.cpp
# Author: Kevin Harris (kevin@codesampler.com)
# Last Modified: 03/25/05
# Description: This sample demonstrates how to perform alpha blending using
# the alpha channel of a standard .tga texture. For proper
# alpha blending, the sample uses a cull-mode sorting trick
# to ensure the sides of the textured cube get rendered in
# back-to-front order.
#
# Control Keys: b - Toggle blending
# s - Toggle usage of cull-mode sorting trick
# Up Arrow - Move the test cube closer
# Down Arrow - Move the test cube away
#-----------------------------------------------------------------------------
#
# Original C++ code by Kevin Harris (kevin@codesampler.com)
# See www.codesampler.com for the original files
# OpenGL samples page 3: Alpha Texture Blending
# http://www.codesampler.com/oglsrc/oglsrc_3.htm#ogl_alpha_blending_texture
#
# Modified for Tcl3D by Paul Obermeier 2008/05/01
# See www.tcl3d.org for the Tcl3D extension.
package require Tk
package require Img
package require tcl3d
# Font to be used in the Tk listbox.
set g_listFont {-family {Courier} -size 10}
set g_WinWidth 640
set g_WinHeight 480
set g_bBlending true
set g_bSortUsingCullModeTrick true
set g_fDistance -4.5
set g_fSpinX(1) 0.0
set g_fSpinY(1) 0.0
# Array of texture coordinates and vertices (GL_T2F_V3F)
# for glInterleavedArrays call.
set g_cubeVertices [tcl3dVectorFromArgs GLfloat \
0.0 0.0 -1.0 -1.0 1.0 \
1.0 0.0 1.0 -1.0 1.0 \
1.0 1.0 1.0 1.0 1.0 \
0.0 1.0 -1.0 1.0 1.0 \
\
1.0 0.0 -1.0 -1.0 -1.0 \
1.0 1.0 -1.0 1.0 -1.0 \
0.0 1.0 1.0 1.0 -1.0 \
0.0 0.0 1.0 -1.0 -1.0 \
\
0.0 1.0 -1.0 1.0 -1.0 \
0.0 0.0 -1.0 1.0 1.0 \
1.0 0.0 1.0 1.0 1.0 \
1.0 1.0 1.0 1.0 -1.0 \
\
1.0 1.0 -1.0 -1.0 -1.0 \
0.0 1.0 1.0 -1.0 -1.0 \
0.0 0.0 1.0 -1.0 1.0 \
1.0 0.0 -1.0 -1.0 1.0 \
\
1.0 0.0 1.0 -1.0 -1.0 \
1.0 1.0 1.0 1.0 -1.0 \
0.0 1.0 1.0 1.0 1.0 \
0.0 0.0 1.0 -1.0 1.0 \
\
0.0 0.0 -1.0 -1.0 -1.0 \
1.0 0.0 -1.0 -1.0 1.0 \
1.0 1.0 -1.0 1.0 1.0 \
0.0 1.0 -1.0 1.0 -1.0 \
]
# Determine the directory of this script.
set g_scriptDir [file dirname [info script]]
# Show errors occuring in the Togl callbacks.
proc bgerror { msg } {
tk_messageBox -icon error -type ok -message "Error: $msg\n\n$::errorInfo"
exit
}
# Print info message into widget a the bottom of the window.
proc PrintInfo { msg } {
if { [winfo exists .fr.info] } {
.fr.info configure -text $msg
}
}
proc SetMouseInput { btn x y } {
set ::g_LastMousePosX($btn) $x
set ::g_LastMousePosY($btn) $y
}
proc GetMouseInput { btn x y } {
set nXDiff [expr ($x - $::g_LastMousePosX($btn))]
set nYDiff [expr ($y - $::g_LastMousePosY($btn))]
set ::g_fSpinX($btn) [expr $::g_fSpinX($btn) - $nXDiff]
set ::g_fSpinY($btn) [expr $::g_fSpinY($btn) - $nYDiff]
set ::g_LastMousePosX($btn) $x
set ::g_LastMousePosY($btn) $y
.fr.toglwin postredisplay
}
proc ToggleBlending {} {
set ::g_bBlending [expr ! $::g_bBlending]
.fr.toglwin postredisplay
}
proc ToggleCullModeTrick {} {
set ::g_bSortUsingCullModeTrick [expr ! $::g_bSortUsingCullModeTrick]
.fr.toglwin postredisplay
}
proc MoveCam { zoff } {
set ::g_fDistance [expr $::g_fDistance + $zoff]
.fr.toglwin postredisplay
}
proc LoadTexture {} {
set texName [file join $::g_scriptDir "radiation_box.tga"]
set retVal [catch {set phImg [image create photo -file $texName]} err1]
if { $retVal != 0 } {
error "Error reading image $texName ($err1)"
} else {
set w [image width $phImg]
set h [image height $phImg]
set n [tcl3dPhotoChans $phImg]
set pTextureImage [tcl3dVectorFromPhoto $phImg]
image delete $phImg
}
set ::g_textureID [tcl3dVector GLuint 1]
glGenTextures 1 $::g_textureID
glBindTexture GL_TEXTURE_2D [$::g_textureID get 0]
glTexParameteri GL_TEXTURE_2D GL_TEXTURE_MIN_FILTER $::GL_LINEAR
glTexParameteri GL_TEXTURE_2D GL_TEXTURE_MAG_FILTER $::GL_LINEAR
if { $n == 3 } {
set type $::GL_RGB
} else {
set type $::GL_RGBA
}
glTexImage2D GL_TEXTURE_2D 0 $n $w $h 0 $type GL_UNSIGNED_BYTE $pTextureImage
$pTextureImage delete
}
proc CreateCallback { toglwin } {
LoadTexture
glClearColor 0.35 0.53 0.7 1.0
glEnable GL_TEXTURE_2D
glMatrixMode GL_PROJECTION
glLoadIdentity
gluPerspective 45.0 [expr double($::g_WinWidth)/double($::g_WinHeight)] \
0.1 100.0
}
proc ReshapeCallback { toglwin { w -1 } { h -1 } } {
set w [$toglwin width]
set h [$toglwin height]
glViewport 0 0 $w $h
glMatrixMode GL_PROJECTION
glLoadIdentity
gluPerspective 45.0 [expr double($w)/double($h)] 0.1 100.0
}
proc DisplayCallback { toglwin } {
glClear [expr $::GL_COLOR_BUFFER_BIT | $::GL_DEPTH_BUFFER_BIT]
# Viewport command is not really needed, but has been inserted for
# Mac OSX. Presentation framework (Tk) does not send a reshape event,
# when switching from one demo to another.
glViewport 0 0 [$toglwin width] [$toglwin height]
glMatrixMode GL_MODELVIEW
glLoadIdentity
glTranslatef 0.0 0.0 $::g_fDistance
glRotatef [expr {-1.0 * $::g_fSpinY(1)}] 1.0 0.0 0.0
glRotatef [expr {-1.0 * $::g_fSpinX(1)}] 0.0 1.0 0.0
# Transparency sorting for our cube...
#
# If you have a single transparent object, or multiple transparent objects
# which do not overlap in screen space (i.e., each screen pixel is touched
# by at most one of the transparent objects), there's a sorting short-cut
# which can be used under certain conditions.
#
# If your transparent objects are closed, convex, and viewed from the
# outside, culling may be used to draw the back-facing polygons prior to
# the front-facing polygons. This will accomplish the same thing
# as sorting your objects or polygons into back-to-front order.
# Fortunately for us, our cube is a perfect candidate for this sorting
# trick.
#
# On the other hand, If we can't use the cull-mode sorting trick, we would
# need to sort our objects manually, which would require us to transform
# the geometry into eye-space so we could compare their final position
# along the z axis. Only then, could we could render them in the proper
# back-to-front order for alpha blending.
#
# Also, if transparent objects intersect in any way, the individual
# triangles of the objects touching will have to be sorted and drawn
# individually from back-to-front. And is some rare cases, triangles that
# intersect each other may have to be broken into smaller triangles so they
# no longer intersect or blending artifacts will persist regardless of our
# sorting efforts.
#
# Its plain to see, transparency sorting can become a big, hairy mess
# real quick.
#
# http://www.opengl.org/resources/tutorials/sig99/advanced99/notes/node204.html
#
if { $::g_bBlending } {
# Use the texture's alpha channel to blend it with whatevers already
# in the frame-buffer.
glDisable GL_DEPTH_TEST
glEnable GL_BLEND
glBlendFunc GL_SRC_ALPHA GL_ONE_MINUS_SRC_ALPHA
glBindTexture GL_TEXTURE_2D [$::g_textureID get 0]
if { $::g_bSortUsingCullModeTrick } {
# Use the cull-mode sorting trick for convex non-overlapping
# geometry.
glEnable GL_CULL_FACE
# Render the cube but only render the back-facing polygons.
glCullFace GL_FRONT
glInterleavedArrays GL_T2F_V3F 0 $::g_cubeVertices
glDrawArrays GL_QUADS 0 24
# Render the cube again, but this time we only render the
# front-facing polygons.
glCullFace GL_BACK
glInterleavedArrays GL_T2F_V3F 0 $::g_cubeVertices
glDrawArrays GL_QUADS 0 24
glDisable GL_CULL_FACE
} else {
# Do no sorting and hope for the best. From certain viewing
# positions the cube's sides will appear sorted correctly, but this
# is typically rare and the cube will not look right most of the
# time.
glInterleavedArrays GL_T2F_V3F 0 $::g_cubeVertices
glDrawArrays GL_QUADS 0 24
}
} else {
# Render the cube, but do no blending...
glDisable GL_BLEND
glEnable GL_DEPTH_TEST
glBindTexture GL_TEXTURE_2D [$::g_textureID get 0]
glInterleavedArrays GL_T2F_V3F 0 $::g_cubeVertices
glDrawArrays GL_QUADS 0 24
}
$toglwin swapbuffers
}
proc Cleanup {} {
if { [info exists ::g_textureID] } {
glDeleteTextures 1 [$::g_textureID get 0]
$::g_textureID delete
}
$::g_cubeVertices delete
foreach var [info globals g_*] {
uplevel #0 unset $var
}
}
proc ExitProg {} {
exit
}
frame .fr
pack .fr -expand 1 -fill both
togl .fr.toglwin -width $g_WinWidth -height $g_WinHeight \
-double true -depth true \
-createcommand CreateCallback \
-reshapecommand ReshapeCallback \
-displaycommand DisplayCallback
listbox .fr.usage -font $::g_listFont -height 6
label .fr.info
grid .fr.toglwin -row 0 -column 0 -sticky news
grid .fr.usage -row 1 -column 0 -sticky news
grid .fr.info -row 2 -column 0 -sticky news
grid rowconfigure .fr 0 -weight 1
grid columnconfigure .fr 0 -weight 1
set appTitle "Tcl3D demo: CodeSampler's Texture Alpha Blending"
wm title . $appTitle
# Watch For ESC Key And Quit Messages
wm protocol . WM_DELETE_WINDOW "ExitProg"
bind . <Key-Escape> "ExitProg"
bind . <Key-b> "ToggleBlending"
bind . <Key-s> "ToggleCullModeTrick"
bind . <Key-Up> "MoveCam -0.1"
bind . <Key-Down> "MoveCam 0.1"
bind .fr.toglwin <1> "SetMouseInput 1 %x %y"
bind .fr.toglwin <B1-Motion> "GetMouseInput 1 %x %y"
.fr.usage insert end "Key-Escape Exit"
.fr.usage insert end "Key-b Toggle blending"
.fr.usage insert end "Key-s Toggle cull mode trick"
.fr.usage insert end "Key-Up Increase distance"
.fr.usage insert end "Key-Down Decrease distance"
.fr.usage insert end "Mouse-L Rotate cube"
.fr.usage configure -state disabled
PrintInfo [tcl3dOglGetInfoString]
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