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EECS 487 PA3: Buffers, Textures, Shaders

EECS 487 PA3: Buffers, Textures, Shaders

This assignment is due on Fri., Nov. 20, 2014 at 10:00 pm

Plain Page for Printing

Overview

In this assignment you will create a scene consisting of multiple spheres and cubes, apply a different texture to each object, and give a bumpy-looking appearance to each surface using normal mapping. You will also get a chance to exercise your understanding of vertex-array object, the use of shader custom vertex attributes and texture samplers, and the use of multiple texture units.

Graded tasks summary (100 points)

  1. Transfer your vertex-buffer object code from Lab 6: Textures and Mapped PBO to the provided support code. (5 points)
  2. Create and texture a cube: fill out init_cube() and draw_cube(), both in objects.cpp. (15 points)
  3. Use vertex-array object to alternately display a sphere or a cube. (5 lines in init_world() and 2 lines in draw_world(), both in objects.cpp). (10 points)
  4. Load multiple textures and texture the objects in task 2 using a different texture for each object. (3 lines in scene.cpp:init_texture() and 2 lines in objects.cpp:draw_world()). (10 points)
  5. Replace client-side vertex attribute with shader attributes (objects.cpp:init_{sphere,cube}(), nmap.vs). (10 points)
  6. Use shader texture samplers (2 lines in scene.cpp:init_textures(), 2 lines in nmap.vs, 3 lines in nmap.fs, and at least 4 lines in objects.cpp:init_{sphere,cube}()). (15 points)
  7. Use multiple texture units and implement normal mapping. (25 points)
  8. Make a scene that incoprates at least 3 objects consisting of normal-mapped sphere(s) and cube(s). Preferably the scene tells a story or expounds upon a concept. (10 points)
The tasks above build on each other, so you should finish debugging one task before moving on to the next task. You may not be able to return to work on the previous task once you have started on the next one.

Implementation details

TASK 1: Vertex-Buffer Object

This assignment builds upon Lab 6: Textures and Mapped PBO. As with PA1, your first task is to transfer your Lab 6 solution to the provided support code. You will be modifying files scene.cpp and objects.cpp for this task. Your solution to Lab 6 is required to have used GL_TRIANGLE_STRIP instead of GL_QUADS. All vertex attributes (position, color, normal, tangent, texture coordinates) must use vertex-buffer object with mapped buffer instead of copying from client-side vertex arrays or using immediate mode. If you are not able to complete Lab 6, you may use our solution instead. However, we will not be making the solution available until after Lab 6 is due and you will be forfeiting the 5 points of this task.

As usual, the provided code files are commented to mark the locations of each task. They also come with sometimes helpful remarks and hints. After you have completed Task 1, running the provided code using the command line: scene -t images/BlueMarble2004-08.tga renders one of the following images. The image is generated by modulating the texture with surface shading instead of just replacing it. All keyboard shortcuts controlling modeling transforms from Lab 6 apply.

Visual Studio: to process the commad line options, we use the getopt() API. If you're building on Windows with Visual Studio, you need to add common/src/wingetopt.c and common/src/wingetopt.h to your project. You may also need to tell Visual Studio the location of wingetopt.h. If you don't know how to do that, please consult the course note on the topic.

TASK 2: Cube rendering

Your second task is to render and texture a cube using client-side vertex attributes. Review the code in init_sphere() and draw_sphere() and adapt them to draw a cube. Modern OpenGL no longer supports GL_QUADS, thus you must use GL_TRIANGLES to model your cube. The important thing to remember here is that you want your cube to have sharp edges. Polygons sharing a cube edge all face different directions, so the normals of shared vertices should not be averaged. In modeling your cube, you must use vertex-buffer object with mapped buffer instead of copying from client-side vertex array or using immediate mode. After you've completed init_cube() and draw_cube() in object.cpp, set drawobject=CUBE in scene.cpp:main() before re-building the binary. Upon completion of this task, running the program with the "Blue Marble" texture should render this image (the orientation of the texture doesn't matter):

TASK 3: Vertex-array object

In this program we recognize only three shape alternatives: SPHERE, CUBE, and NOBJS, where NOBJS means both sphere and cube (see objects.h). Your third task is to encapsulate all the states for rendering each shape in a vertex-array object. This is accomplished in objects.cpp:init_world() by first generating NOBJS vertex-array objects, then binding to the vertex-array object for SPHERE before calling init_sphere(), and then binding to the vertex-array object for CUBE before calling init_cube(). To enable alternate rendering of the sphere and cube, in objects.cpp:draw_world(), bind to the corresponding vertex-array object before calling draw_sphere() or draw_cube(). You may use a global array to hold the vertex-array object handles so that they are accessible in both init_world() and draw_world() functions. Set drawobject=NOBJS in scene.cpp:main() before re-building the binary. When you run the updated program, you'll see a blank, black screen. Pressing the 'b' or 'c' key renders a sphere or a cube as shown above respectively.

TASK 4: Multiple texture objects

As is, scene.cpp:init_textures() creates ntexs number of texture objects, but the code from Lab 6 loads only a single texture. Modify the function such that it loads ntexs number of textures into as many texture objects. Then in objects.cpp:draw_world() bind with the corresponding texture before calling draw_sphere() and draw_cube(). Run the updated program with two different textures, e.g., scene -t images/BlueMarble2004-08.tga -t images/borg_Celtic_Entropy.tga. You'll see a blank, black screen; pressing the 'b' or 'c' key renders a sphere or a cube as before, but each textured differently.

TASK 5: Shader custom vertex attributes

The provided, skeletal vertex shader nmap.vs uses client-side vertex attributes such as gl_Vertex and gl_Normal to perform its computations. Modify nmap.vs to use custom vertex attribute variables for vertex position and vertex normal. In objects.cpp:init_sphere(), first get the location of the custom vertex attributes using glGetAttribLocation(), then enable the vertex attributes and pass the corresponding attribute arrays to the shader using glEnableVertexAttribArray() and glVertexAttribPointer(). The shader program handler that you need to set the custom vertex attributes is declared as a global variable (spd) in scene.cpp. Near the top of scene.cpp replace the default shader_mode from NONE to NMAP to have the program load your shaders instead of using the fixed-function pipeline. You should be able to build an updated program that renders an untextured sphere when 'b' is pressed. Similarly enable vertex position and normal attributes in init_cube() to render an untextured cube when pressing 'c'.

As of OpenGL 3.1, using vertex-array objects, vertex-buffer objects, and custom vertex attribute locations is considered the ``correct'' way of passing vertex attributes from the application to the shader. With OpenGL ES (WebGL), this is the only way. The way we passed vertex attributes in lab5 and lab6 and prior to this task are considered "deprecated."

TASK 6: Shader texture sampler

Modify objects.cpp:init_sphere() to pass texture coordinates to the shader as a vertex attribute. Similarly, modify object.cpp:init_cube(). In nmap.vs, pass the texture coordinates attribute as a varying variable to the fragment shader. In scene.cpp:init_textures() use glGetUniformLocation() and glUniform1i() to get the texture sampler location and specify texture unit 0 as the texture sampler. In nmap.fs declare the texture sampler as a uniform variable to be set by the application and the texture coordinates as a varying variable to be passed in by the vertex shader. Then sample the texture at the texel specified by the texture coordinates and compute lighting at the fragment using the texel. Running the updated program with scene -t images/BlueMarble2004-08.tga -t images/borg_Celtic_Entropy.tga and pressing "b' and 'c' should render the following images respectively.

TASK 7: Multitexturing and Normal Mapping

Normal maps can be specified on the command line using the -n option, e.g., scene -t images/BlueMarble2004-08.tga -n images/BlueMarble2--4=08-Normal.tga. If multiple texture and normal maps are specified, the program pairs them up in order. In scene.cpp:init_nmaps() load the normal maps into texture unit 1. This function pretty much duplicates scene.cpp:init_textures() except you need to call glActiveTexture() before creating the texture objects and loading the texture files. It is made a separate function from init_textures() simply for ease of separating the tasks in this assignment. In objects.cpp:draw_world(), for each texture unit, bind the appropriate texture object you have intended for each shape before calling its draw function.

You may want to review the lecture notes on normal mapping. As explained in the lecture notes, the next step is to compute a tangent per vertex. If a vertex is shared by multiple polygons forming a curved surface, you most likely want to compute an average tangent for the vertex, including at the seam where the texture wraps around and meets itself. Modify your code in objects.cpp:init_sphere() and objects.cpp:init_cube() to compute and pass along per vertex tangent to the vertex shader. You would need to add the tangent attribute to the sphere_vertex_t structure (and the corresponding structure for your cube). Figuring out how to compute average tangent per vertex could be rather time consuming (though it's more straightforward for cube than for sphere). For that reason, you may want to complete the earlier tasks as soon as they have been covered in lecture and not wait for the last week before the due date to start this assignment.

In nmap.vs use the tangent and normal vertex attributes to compute the bitangent at the vertex and compute an orthonormal TBN matrix. Use the inverse of the TBN matrix to transform the light and view vectors to tangent space and pass them to the fragment shader. In nmap.fs, sample the normal map passed in by the application at the texture coordinates passed in by the vertex shader (the same ones used to sample the texture map) and use the sample from the normal map as the per-fragment normal. Using the view and light vectors in tangent space passed in by the vertex shader, along with the sampled normal, compute the per-fragment lighting. Modulate the computed light with the texel sampled from the texture map to shade each fragment. The following images show the "BlueMarble" texture mapped onto a cube face with and without normal mapping respectively. Note the extra details in north Africa, for example, in the image rendered with normal mapping.

TASK 8: Make a scene!

Let your creativity loose and create a scene involving at least 3 objects incorporating both spheres and cubes. Remember that you can shear the shapes or apply other transforms to them. To get full credit, your scene must (1) show off normal mapping and (2) use texture and normal maps other than the ones provided (if I forgot to show how to create normal maps using gimp, please ask). Don't skip this step! Even if you have completed only the first three tasks, if your scene is compelling enough, you will get partial credit for this. Below is an obvious example scene (you have to come up with something better!). Running your program should now show your scene. To help debug each individual shape, you can switch to showing only the first sphere or the first cube by pressing 'b' or 'c' respectively. Pressing 'a' returns you to full scene rendering.

Submission Guidelines

As with PA1, to incorporate publicly available code in your solution is considered cheating in this course. To pass off the implementation of an algorithm as that of another is also considered cheating. For example, if the assignment asks you to implement sort using heap sort and you turn in a working program that uses insertion sort in place of the heap sort, it will be considered cheating. If you can not implement a required algorithm, you must inform the teaching staff when turning in your assignment, e.g., by documenting it in your writeup.

Test the compilation!
Code that does not compile will be heavily penalized.

The creative portion of this project, Task 8, will take a long time if you are interested in getting a good grade. This involves a lot of trial and error. Remember that to get full credit for this task, your scene must (1) show off normal mapping and (2) not use the provided texture and normal maps. Post the image(s) from your Task 8 to the course's Image Gallery by logging in to a CAEN linux machine and running the following:

% cd <to where your image.png file is located>
% /afs/umich.edu/class/eecs487/scripts/postimg <image.png> [<image2.png ...>]

Create a writeup in text format that discusses:

  1. Your platform and its version: Linux, Mac OS X, Windows, or any other.
  2. Anything noteworthy about your implementation, e.g., if you implemented cube mapping.
  3. URL of any web site you reference, either for texture, normal map, or cube modeling.
  4. Feedback on the assignment.
  5. Name the file writeup-uniqname.txt.
    For example, the person with uniqname tarukmakto would create writeup-tarukmakto.txt.
Your "PA3 files" consists of your writeup-uniqname.txt, scene.cpp, objects.cpp, nmap.vs, nmap.fs, and any texture and normal map files you created or used for Task 8.

To turn in your PA3, upload a zipped or gzipped tarball of your PA3 files to the CTools Drop Box. Keep your own backup copy! The timestamp on your uploaded file will be your time of submission. If this is past the deadline, your submission will be considered late. You are allowed multiple "submissions" without late-policy implications as long as you respect the deadline.

Turn in ONLY the files you have modified. Do not turn in support code we provided that you haven't modified. Do not turn in any binary files (object, executable, dll, or library files) with your assignment. Your code must not require other external libraries and include files other than the ones listed in the Makefile.

Do remove all printf()'s or cout's and cerr's you've added for debugging purposes.

General Information

The General Information section from PA1 applies. Please review it if you haven't read it or would like to refresh your memory.