Project 1 Help Session

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Outline

• Assignment overview
• The /usr/class/cs348b tree
• Going from the xsupport example program to a working raytracer
• what's provided: example.c
• what you have to write
• composer constants
• FAQ

Assignment overview

• C or C++:
• Read the README files in /usr/class/cs348b/
• Only need to handle spheres and triangles
• HW1: One material per object, per-face normals
• HW2: per-vertex normal, material
• Don't optimize yet

The /usr/class/cs348b tree

• README
• README.composer
• README.submit
• README.xsupport
• README.porting
• bin/
(only on SGIs)
• composer
• i3dm
• i3dm_clean
• iv2out (ignore)
• out2out (ignore)
• snoop
• supersnoop
• submit
• example/
• (start here -- copy to your directory)
• (uses scene_io and xsupport)
• include/
• scene_io.h
• xsupport.h
• init/
• (source init.csh)
• lib/
• XXX/libxsupport.a
• proj1/
• README
• tests/
• README
• testx.iv
• testx.out
• testx.rgb
• resources/
• XXX/Xresources (used by cs348b/init/init.csh)
• tools/
• composer/ (includes source code)
• iv2out/ (ignore)
• out2out/ (ignore)
• soft2out/ (ignore)
• i3dm/
• models/
• movies/
• textures/
• (John Kichury's modelling package supporting materials)
• useful-code/
• README
• (Graphics Gems vector and matrix algebra routines)
• xsupport/
• obj/
• src/
• (Source to recompile xsupport, to run on other platforms)
• (Uses Motif widget library)

Going from the xsupport example program to a working raytracer

• What's provided: example.c
• Demonstrates widgets for your control box
• Starts with two Canvases
• ReadComposer() and LoadScene(char *name)
• Reads scene (e.g. testx.out)
• (see /usr/class/cs348b/include/scene_io.h for data structures)
• structures: SceneIO, CameraIO, LightIO, ObjIO, MaterialIO, VertexIO, PolygonIO
• writes scene out in ASCII (to verify it)
• deletes the scene
• LoadPPM()
• SavePPM()
• main()
• Initialize Canvases
• Calls LiftOff()
• After this, user events trigger callback functions
• What you have to write
• Modify control widgets to do meaningful things, such as control ray tree depth and image size
• Modify ReadComposer() and LoadScene(char *name) so that you don't delete the scene immediately
• Write Render()
• Chap 7 Sec 3 by Heckbert in Glassner book is your friend
• Screen, Trace, Shade, Intersect
• raytrace the scene to the canvas image buffer
• UpdateCanvas(), so you can see the image
• Composer constants

(from README.composer)
• Whitted's Eqn (16.55 of FvDH):

I = k_a I_a O_d + Sum_i ( S_i f_atti I_pi [ k_d O_d (N*L_i) + k_s (N*H_i)ⁿ ] ) + k_s I_r + k_t I_t
• (k_d*O_d) is given by "diffColor"
• Composer outputs a single "ambient color", whereas the ambient term in Whitted's equation is given by k_a I_a O_d. We suggest treating the ambient color you get from Composer as I_a and multiplying it by the diffuse color K_d O_d to get your ambient term.
• For (semi-)transparent surfaces, you should probably multiply the diffuse and ambient terms by (1-k_t). Otherwise, the diffuse and transmitted rays will add up, and the surface will become washed-out.
• k_s is given by "specColor". Note that the latter is a vector which has all three values identical. This value is k_s. The redundancy is being maintained for historical reasons.
• For assignment 1, always use a refractive index of 1.5 where applicable.
• Ignore the emissive component output by composer.
• For ⁿ, use shininess*128 (where shininess is composer's shininess output between 0 and 1).
• For f_att (attenuation of light sources), use FvDFH equation 16.8 ( f_att = min(1, 1 / ( c₁ + c₂ d_L + c₃ d_L² ) ), with c₁ = 0.25, c₂ = 0.1 and c₃ = 0.01. (If your results don't look satisfactory to you, feel free to play with this parameter). Secondary rays (reflected and transmitted rays) are not attenuated.
• Use an aspect ratio of 1 for the screen.
• The ambient colors and headlight strength output by Composer may be scaled such that if you blindly implement Whitted's equation, your scenes may appear washed out. Scale these factors until your ray traced image looks roughly similar to the sample images in /usr/class/cs348b/proj1/tests.