Normals and the World Inverse Transpose Matrix

On the last assignment and in the exam review, there was a question about the world inverse transpose matrix.  I perused a bunch of online material on this issue, and thought this discussion had a good explanation:

The purpose of transforming a normal by the world matrix is to rotate it so that it's a direction in world-space.  This is typically done by only using the 3x3 portion of the world matrix, since this includes all of the rotation data and none of translation (you don't want to translate a normal). 

The 3x3 portion of the matrix also can contain scaling data.  When it contains scaling data, the normal is scaled by the scaling factor.  As long as the scale is uniform (which means that xScale == yScale == zScale), the scaling is okay provided your normalize the resultant normal vector before using it.  However if the scale is non-uniform, this won't work.  The solution in the case of non-uniform scaling is to calculatate the inverse transpose outside the shader, pass it in, and then transform normals (and also tangents/bitangents, if necessary) by that matrix.

So in summary:  if you're using no scaling or uniform scaling in your world matrix you can use the world matrix, if you're using non-uniform scaling then you need to use the inverse transpose.

So, in part 4 of the last assignment, changing the scaling of the sphere to be non-uniform caused the normals to be incorrect until you used the inverse transpose world matrix instead of the world matrix.

Tutorial: Tuesday at 1pm

Our informal tutorial is going to be Tuesday at 1pm.  I will edit this post with a room as soon I have one.  Be sure to submit questions ahead of time so I can prepare the best answers possible. :)

Update: We will meet at my lab, 5317 HP, at 1pm.

Exam Review Tutorial

If you are interested in attending a review session, please fill in the poll linked to below.  Only choose times you know you can attend. I need at least five people to make it worthwhile.

Tutorial Scheduling Poll

Also, please submit questions or topics you would like to be covered in the tutorial so I can prepare good answers for you ahead of time.  You can submit as many times as you like, but be specific, and only ask the most important things (otherwise I'll run out of time to help you with them!).

Tutorial Questions Form

Modifying the Shader Example for Assignment 5

Here are the steps I took to modify the crater shader example available on the course web page to make a wave effect.  This is part of what you had to do for Assignment 5.

• Removed warnings. ;)
   
• In the mesh_wave.fx file added in the following:
  uniform extern texture gWorldTex;
  uniform extern float3 direction;
  uniform extern int amplitude;
  uniform extern float wavelength;
   
• Added the following sampler info structure for use with textures:
  sampler2D mySampler = sampler_state {
      Texture = (gWorldTex);
      MinFilter = Linear;
      MagFilter = Linear;
      AddressU = Wrap;
      AddressV = Wrap;
  };
    
• Added or modified the following structs to the effect file:
  
  struct inputVS {
      float3 pos : POSITION0;
      float4 col : COLOR0;
      float2 tex0: TEXCOORD0;
  };
  
  struct OutputVS {
      float4 pos : POSITION0;
      float4 col : COLOR0;
      float2 tex0: TEXCOORD0;
  };
   
• Added a new vertex shader in the effect file called directionalWaveVS:
   
• used the following formula to determine the distance from the plane with the normal given by the direction passed in:
  d = direction.x * vin.pos.x + direction.z * vin.pos.z;
   
• used the following formula to compute the new y position of the current vertex being processed, using the distance computed above and an omega value of 0.07:
  vin.pos.y += amplitude*cos(wavelength*d-omega*time);
   
• transformed the current vertex using the world, view, and projection matrices
   
• saved the input colour and texture value to be passed along to the pixel shader
   
• Modified the pixel shader function to use the texture's colour instead of the vertex's colour. Used the following function with the input texture coordinate to accomplish this:
  tex2D(mySampler, v.tex0)
   
• Added a wavesTechnique that uses the new vertex and pixel shaders in a single pass.
   
• Added "waveTechnique" to the techniceName array (ignoring the misspelling...)
   
• Added D3DXVECTOR2 tex0 to meshVertex in meshSurface.h
   
• Added int amplitude, float waveDir and float waveLength to the meshSurface class, and initializing these values in the constructor (good defaults are amplitude=50, wavelength=0.01f, and waveDir=0.0f)
   
• Added D3DXHANDLE hWaveTechnique, D3DXHANDLE hDirection, D3DXHANDLE hAmplitude, and D3DXHANDLE hWavelength to the meshSurface class
   
• Added the following to the D3DVERTEXELEMENT9 decl in meshSurface.cpp:
  {0,0,D3DDECLTYPE_FLOAT2, D3DDECLMETHOD_DEFAULT, D3DDECLUSAGE_TEXCOORD, 0}
   
• And after that, assuming it was placed third in decl:
  decl[2].Offset = (char *) &v.tex0 - (char *) &v;
   
• Set up texture usage (mTexture is already declared in the class):
   
• released mTexture in the class destructor
• updated the texture coordinates in the vertex structure in createSurface:
  vtx[k].tex0.x = texU;
  vtx[k].tex0.y = texV;
• created the texture in initEffect:
  hTexture = pMeshEffect->GetParameterByName(NULL, "gWorldTex");
  D3DXCreateTextureFromFile(md3dDev, "earth.bmp", &mTexture);
• Associated the direction, amplitude, and wavelength variables with their counterparts in the effects file in initEffect:
  hDirection = pMeshEffect->GetParameterByName(NULL, "direction");
  hAmplitude = pMeshEffect->GetParameterByName(NULL, "amplitude");
  hWavelength = pMeshEffect->GetParameterByName(NULL, "wavelength");
   
• Associated the new wave technique in the effects file in initEffect:
  hTechnique = pMeshEffect->GetTechniqueByName(techniceName[0]);
   
• Updated ShaderRender to compute the application-side values needed for the effect file:
   
• computed the wave's direction (making sure to initialize the wave direction at some point - can default to zero, and if desired, can be controlled with keyboard input):
  float directionVec[3] = {sin(waveDir), 0.0f, cos(waveDir)}
   
• copy the texture, direction, amplitude, and wavelength values into their counterparts in pMeshEffect
   
• set the technique to the waves technique:
  pMeshEffect->SetTechnique(hWaveTechnique);

In the effects file, I also added a second wave to add onto the first one and played with the parameters to see what kinds of effects it gave me.  You can uncomment that line to see for yourself.

Game Design Document Comments

After submitting your grades (as assigned by the prof) and adding my own comments on WebCT, I thought I'd share some general comments and advice here.

I realize that some of my suggestions might be out of date since you've likely made progress since that document, but I'll share just in case you haven't, and to give you something to think about for the next time.

First, something I suggested to most if not all of you is to sketch out your levels.  It was clear in the design documents that most of you did not have a concrete idea of how the levels would look yet, so this will be a crucial step.  You will end up with a much better design if you work on it on paper before diving into implementation, and it will give you something useful for the final report.

Second, I tried to suggest ways to come up with a minimally viable product that you could submit.  For instance, spending lots of time on artwork when the very basics of the game are not yet working is not a good idea.  You need to know what the must-haves are, and then prioritize the rest after that.  I'd be happy to discuss ideas related to this if you want to.

Finally, something I didn't write much in the comments is to make good use of your resources - especially me and the prof! Here is how you can approach getting my help to get the most out of it:

• Send me an email with lots of context.  What are you working on? What are trying to accomplish? What have you tried so far? Are you stuck halfway through, just need a bit of help debugging, or don't even know where to start?
   
• You may want to include code.  Sometimes pasting a snippet will be enough, but sometimes you'll have to send the whole project for context.  If you do, make sure to remove build files and minimize the zip file size, and even more importantly, tell me where to look in the code.
   
• If you want to meet in person, there are some office hours left, but not many.  It helps to send an email to say you are coming so I can let you know if there are any other students around and when you should come.  After office hours are over, I may be able to help out on an appointment basis, but you will need to give lots of notice for that to happen.

I think that's about it - good luck everyone! I am looking forward to seeing your games! :)

An Applet For Diffuse, Ambient, and Specular Lighting

Since you either have covered this recently or will very soon, I will repost this information about lighting from last year's blog in case it helps you out.

I have another applet I wrote a while back that might be useful to you. It demonstrates the various kinds of lighting and can really help you understand what's happening behind the equations.  

In class you learned about diffuse, ambient, and specular lighting.  Diffuse lighting comes from a direct light source like the sun, while ambient lighting is just what's hanging around in the environment.  Highlights on a surface from the direct light source appear as specular highlights and depend on where your eye is positioned relative to the surface.

In my applet, you can adjust the intensities of the red, green, and blue light coming from the ambient and direct light sources.  You can also adjust the surface reflectance, which determines how much of a certain colour of light will be reflected back from the surface (and eventually reach your eye, making the material look like a certain colour).  If the surface does not reflect any blue, then changing the blue intensity on the lights won't affect anything (the only exception being for the specular highlight, since those are made before the light would be absorbed/reflected in the surface anyway).

You can move the sun (direct light source) and the eye (viewpoint/camera centre), and you can tilt the surface to see how the angle between its normal and the other directions changes the outcome.

I recommend trying to isolate each type of light first to see how they look.  Turn the specular highlight off at first as well.  Then try to compare what you see with the equations involved in defining the light sources.

As always, if you have any questions, comment here or email me!

Go to the applet now...

Assignment 4 Marking Scheme

Here is the marking scheme I used to grade Assignment 4, along with details of the desired solution for Task 1:

 

Task 1 (30%)

• If you said something correct but fairly obvious and simple (such as 'rotating the camera around the vector'), you will get only 10%
• If you did a little better than the minimal description, but wrote something that didn't require you to understand more deeply what the code was doing and why, you will get 15%
• I am looking for a much more detailed description of all the steps involved; I want to know that you understood it beyond what each line of code has done (for instance, I want to know you understand what the role of the up and lookat vectors actually are for, and how/why we want to change them in the context of the overall game).  Also, why the function is needed goes beyond code organization; I wanted to know why the stuff done in the function is needed.
• Here is a sample response (something closer to this would get you full marks):
• This function adjusts the orientation (i.e. rotation) of the camera in space using the input of a vector representing the axis of rotation and the number of degrees to rotate around it. The camera’s defining members (look-at and view-up vectors) are updated to reflect their new orientation relative to the world. This allows us to simulate pitch, roll, and yaw by rotating around the appropriate axis vector.
• A rotation matrix representing rotation around the input rotVector by angleRad (radians) is created with D3DXMatrixRotationAxis. D3DXVec3TransformCoord applies the rotation matrix to the two defining camera vectors: the view-up vector and the look-at vector. This is enough to say that the camera’s orientation has now been updated since these two vectors completely define that orientation.
• The last set of cross products and normalizations are done to update the up vector. It probably seems odd that we would do this given that we just rotated it (hence it is “updated”), but the reason it is done because of floating point number inaccuracies in the rotations. There’s a good chance the up and look-at vectors will lose their orthogonality over time, so this update ensures they are always orthogonal.

 

Task 2 (35%)

• 5% for implementing each of the functionalities correctly

 

Task 3 (35%)

• 5% each for correctly implementing pitch, yaw, changePositionDelta(D3DXVECTOR3 *dv), changeAbsPoition x 2, moveForward
• an extra 5% for generally having no build errors (3%) or warnings (2%) (as mentioned on course blog); although this wasn't specified in the assignment, I did ask for it on previous assignments and the course blog, and this task didn't divide out to 35 marks nicely

 

Bonus 1 (20%)

• 3% most items, 5% airplane roll angle

An Applet to Help Review 2D Transformations

Here is a post I made to last year's blog that might help you review how 2D transformations work.  I recommend ensuring you have a very good grasp of this now so that you aren't scrambling closer to the final exam.

Before moving on to 3D transformations, you should make sure you have a good handle on the same transformations in 2D.  Earlier this year I had made an applet that lets you play around with the basic transformation matrices - it might be useful to you when reviewing how it all works.

In this applet, an arrow is transformed according to the matrices along the bottom.  You can imagine the points in the arrow being in a matrix to the far right, as would be the case when working these things out on paper.  The right-most matrix is applied first, then the next one to its left, and so on.

You can rearrange the matrices to understand exactly how order matters.  You can also play around with the raw transformation values and see how the matrices are updated.

Press play to see the animation, and stop to reset it and allow you to make further changes.

Go to the applet now...

Comments on Assignments 2 and 3

Assignment 2 was well done by everyone who submitted it.  Assignment 3 had some more issues, which seemed more like a matter of students rushing to get it done than anything else (i.e., sloppiness).  But it was fairly well done, too.

A few things to remember for future assignments:

• PLEASE do these changes to make sure your code compiles on all computers.  Marks will be taken off in the future if your code does not compile for these reasons.  Ask if you need help.
• Also, clear your warnings.  I know they aren't always made by you, but when I see a list of warnings, how will I know from a glance which are yours? It's such a good habit that I will be taking marks off in the future for having warnings.
• Make sure you read the assignment carefully, and put code in the functions it wants you to put it in.  I wasn't checking for that this time around, but will in the future, and will take marks off for not following the directions.

As always, email or comment here if you have any questions or concerns!

Office Hours Friday October 12

I will be on campus tomorrow afternoon, most likely in my lab for most of the time.  If you would like to visit me in person, please email ahead to make sure I will be there.  I should be on campus from 1pm - 3:30pm at least.

As usual, feel free to email for help instead!

Making Assignment 2 Compile

A few of you have had issues making Assignment 2 compile.  There are a couple of steps to making it work, as follow. (You may need to follow these instructions in addition to this.)

First, you will notice there are issues with some include header files.  The include that has a big long path can just be commented out - the needed header file is already included in the correct way after that line.  You can just remove the include for dxerr9.h as it is not needed.

Second, you'll see issues with the house class.  The files you need exist, but they are not included in the project properly.  If you look under "External Dependencies" in the Solution Explorer, you will find House.h.  You can right click that file and add it to the project.  You'll also need the source file, though.  To get that, right click on the "Source Files" folder in the Solution Explorer, then Add, Existing Item... You'll find House.cpp in the first folder that pops up.

At this point everything should be compiling.  Leave a comment or email me if you are still having issues.

Upcoming Office Hours

Hi all! I don't see office hours on the website yet, and things are a bit wonky the next couple of weeks anyway, so I wanted to let you know the current plans.

Oct 1-5: I am away at a conference all week, and won't have any office hours.  However, I can answer emails, hopefully within a day or two max.

Oct 5-9: This week I have to go to a conference in Montreal, but only on Wednesday.  I'll probably have office hours on Friday instead of Wednesday.  You can definitely email and expect a quick response.

Rest of the term: My official office hours are going to be Wednesdays 1:00-3:30 in my lab (5317 HP).  I recommend emailing to set up a time to meet me in case I can spread you out and give you individual attention.  I will always be available for help via email and can usually answer within a day (often much less).

Resources

Here are some resources that might be useful to you now or later in the term...

• Changes to make in project properties to ensure the project builds everywhere
• Open Asset Import Library (mentioned in class)
• Two-Kings DirectX Tutorials
• Toymaker DirectX Tutorials/Information
• 2D Transformations Applet
• Diffuse, Ambient and Specular Lighting Applet

Assignment 1 Marking Scheme and Comments

Assignment 1 has now been graded in WebcT.  Here are some comments and how I assigned grades and some suggestions for the future.

Here is the marking scheme I used:

• In Part 1:
• Worth 40 marks
• -10 if the mouse coordinates are wrong (e.g. don't start from 0,0 in the top left)
• In Part 2:
• Worth 40 marks
• -10 if the mouse coordinates are wrong (but won't take these marks off twice if also wrong in Part 1)
• -20 if both windows work with the right mouse button (instead of one working with the left)
• In Part 3:
• Worth 20 marks
• -20 if it does not appear to be implemented correctly, which includes any window closing even after saying 'no'
• -10 if you applied this part to Part 1 only, since it would be harder to do for Part 2 with the two windows
• If you applied this part to Part 2 only, but it worked right, that's ok since it's the harder part

A suggestion for future assignments: since a marking scheme is (unfortunately) not given  ahead of time, think about what sorts of thing I might look for in the completed assignment.  For simple tasks, I will want to see it working fully the way you'd expect it to as a user, even if it's not specified in the instructions.  For example, for part 3 of this assignment, I don't want my window to close if I say I don't want the application to close.

In general, I want to recommend that everyone clear their warnings, even if you didn't produce them.  It's a good software engineering practice to do this because a bunch of trivial warnings can obscure an important one that comes up later.  I'd like to see no warnings when I compile your project, and may take marks off for having warnings in the future.

If your project folder is big, you may not have deleted the build files before zipping it.  Please make sure you keep the size down by removing the build files before submitting.

Finally, please follow the advice from this post from last year to ensure I don't get build errors - I might be inclined to take marks off for having to fix it in the future. ;)

Welcome

Hello everyone! I decided to start this blog so that we would have a one-stop place for addressing common issues that come up in assignments and course material.  I will try to share useful resources that I've found and write out solutions to issues I think many students may face.  I will also likely post a list of common issues with completed assignments and refer to that list when I return your work.


I recommend checking back often or subscribing to the RSS.

Please feel free to comment here or email me directly with questions.