Jason McKesson avatar Jason McKesson committed c46ce3a

Start of texture tutorial.

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Documents/Illumination/Tutorial 13.xml

 uniform Projection
 {
 	mat4 cameraToClipMatrix;
-};Q
+};
 
 uniform float sphereRadius;
 uniform vec3 cameraSpherePos;

Documents/Texturing.xml

             generate a lighting model. In the very last tutorial, we were able to convincingly
             render a mathematically perfect representation of a sphere simply by rendering two
             triangles.</para>
-        <para>All without textures. Thus, the first lesson this book has to teach you about textures
-            is that they aren't <emphasis>that</emphasis> important. What you have learned is how to
-            think about solving graphics problems without textures.</para>
+        <para>All of this has been done without textures. Thus, the first lesson this book has to
+            teach you about textures is that they aren't <emphasis>that</emphasis> important. What
+            you have learned is how to think about solving graphics problems without
+            textures.</para>
         <para>Many graphics texts overemphasize the importance of textures. This is mostly a legacy
             of the past. In the older days, before the availability real programmable hardware, you
             needed textures to do anything of real importance in graphics rendering. Textures were
             have value in other areas as well. But there is so much more to rendering than textures,
             and this is especially true with programmable hardware.</para>
         <para>A texture is a look-up table; an array. There is a lot of bits of minutiae about
-            accessing them, but at their core, a texture is just a large array of some
-            dimensionality that you can access from a shader. Perhaps the most important lesson you
-            could learn is that textures are tools. Use them where appropriate, but do not let them
-            become your primary solution to any rendering problem.</para>
+            accessing them, but at their core a texture is just a large array of some dimensionality
+            that you can access from a shader. Perhaps the most important lesson you could learn is
+            that textures are tools. Use them where appropriate, but do not let them become your
+            primary solution to any rendering problem.</para>
     </partintro>
+    <xi:include href="Texturing/Tutorial 14.xml"/>
 </part>

Documents/Texturing/Tutorial 14.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<?oxygen RNGSchema="http://docbook.org/xml/5.0/rng/docbookxi.rng" type="xml"?>
+<?oxygen SCHSchema="http://docbook.org/xml/5.0/rng/docbookxi.rng"?>
+<chapter xmlns="http://docbook.org/ns/docbook" xmlns:xi="http://www.w3.org/2001/XInclude"
+    xmlns:xlink="http://www.w3.org/1999/xlink" version="5.0">
+    <?dbhtml filename="Tutorial 14.html" ?>
+    <title>Textures are not Pictures</title>
+    <para>Perhaps the most common misconception about textures is that textures are pictures: images
+        of skin, rock, or something else that you can look at in an image editor. While it is true
+        that many textures are pictures of something, it would be wrong to limit your thoughts in
+        terms of textures to just being pictures. Sadly, this way of thinking about textures is
+        reinforced by OpenGL, since many functions around textures have <quote>image</quote>
+        somewhere in them.</para>
+    <para>The best way to avoid this kind of thinking is to have our first textures be of those
+        non-picture types of textures. So as our introduction to the world of textures, let us
+        define a problem space that textures can solve without having to be pictures.</para>
+    <para>We have seen that the Gaussian specular function is a pretty useful specular function.
+        It's shininess value is a nice (0, 1] value, and it produces pretty good results visually.
+        It has fewer artifacts than the less complicated Blinn-Phong function. But there is one
+        significant problem: Gaussian is much more expensive to compute. Blinn-Phong requires a
+        single power-function; Gaussian requires not only exponentiation, but also an inverse-cosine
+        function. This is in addition to other operations like squaring the exponent.</para>
+    <para>Let us say that we have determined that the Gaussian specular function is good, but too
+        expensive for our needs.<footnote>
+            <para>This is for demonstration purposes only. You should not undertake this process
+                unless you have determined with proper profiling that the specular function is a
+                performance problem that you should work to alleviate.</para>
+        </footnote> So we want to find a way to get the equivalent quality of Gaussian specular but
+        with more performance. What are our options?</para>
+    <para>A common tactic in optimizing math functions is a <glossterm>look-up table</glossterm>.
+        These are arrays of some dimensionality that represents a function. For any function <inlineequation>
+            <mathphrase>F(x)</mathphrase>
+        </inlineequation>, where x is valid over some range [a, b], you can define a table that
+        stores the results of the function at various points along the valid range of x. Obviously
+        if x has an infinite range, there is a problem. But if x has a finite range, one can decide
+        to take some number of values on that range and store them in a table.</para>
+    <para>The Gaussian specular function takes three parameters: the surface normal, the half-angle
+        vector, and the specular shininess of the surface. However, if we redefine the specular
+        function in terms of the dot-product of the surface normal and the half-angle vector, we can
+        reduce the number of parameters to two. Also, the specular shininess has been a constant
+        value across a mesh. So, for any given mesh, the specular function is a function of one
+        parameter: the dot-product between the half-angle vector and the surface normal.</para>
+    <!--TODO: Equation for Gaussian, with a constant shininess and based on the dot-product.-->
+    <para>So how do we get a look-up table to the shader? We could use the obvious method; build a
+        uniform buffer containing an array of floats. We would multiply the dot-product by the
+        number of entries in the table and pick one based on that value. By now, you should be able
+        to code this.</para>
+    <para>But lets say that we want another alternative; what else can we do? We can put our look-up
+        table in a texture.</para>
+    <section>
+        <?dbhtml filename="Tut14 The First Texture.html" ?>
+        <title>The First Texture</title>
+        <para>A <glossterm>texture</glossterm> is an object that contains one or more arrays of some
+            dimensionality. The storage for a texture is owned by OpenGL and the GPU, much like they
+            own the storage for buffer objects. Textures can be accessed in a shader, which fetches
+            data from the texture at a specific location within the arrays. The process of fetching
+            data from a texture is called <glossterm>sampling.</glossterm></para>
+        <para>The arrays within a texture are called <glossterm>images</glossterm>; this is a legacy
+            term, but it is what they are called. Textures have a <glossterm>texture
+                type</glossterm>; this defines characteristics of the texture as a whole, like the
+            number of dimensions of the images and a few other special things.</para>
+        <para>We first use textures in the <phrase role="propername">Basic Texture</phrase>
+            tutorial. This tutorial shows a scene containing a golden infinity symbol, with a
+            directional light and a second moving point light source.</para>
+        <!--TODO: Picture of the tutorial.-->
+        <para>The camera and the object can be rotated, with the left and right mouse buttons
+            respectively. Pressing the <keycap>Spacebar</keycap> toggles between shader-based
+            Gaussian specular and texture-based specular. The <keycap>1</keycap> through
+                <keycap>4</keycap> keys switch to progressively larger textures, so that you can see
+            the effects that higher resolution look-up tables has on the visual result.</para>
+        <section>
+            <title>Building Textures</title>
+            <para>In order to understand how textures work, let's follow the data from our initial
+                generation of the lookup tables to how the GLSL shader accesses them.</para>
+            <para/>
+        </section>
+        <para/>
+        <para/>
+        <para/>
+        <para/>
+        <para>Textures and buffer objects have many similarities. They both represent memory owned
+            by OpenGL. The user can modify this memory with various functions. Besides the fact that
+            a texture object can contain multiple images, the major difference is the arrangement of
+            data as it is stored by the GPU.</para>
+        <para>Buffer objects are linear arrays of memory. The data stored by OpenGL must be
+            binary-identical to how the user specifies the data with
+                <function>glBuffer(Sub)Data</function> calls. The format of the data stored in a
+            buffer object is defined external to the buffer object itself. Buffer objects used for
+            vertex attributes have their formats defined by glVertexAttribPointer. The format for
+            buffer objects that store uniform data is defined by the arrangement of types in a GLSL
+            uniform block. In all cases, it is the <emphasis>user's</emphasis> responsibility to
+            make sure that the data stored there uses the format that OpenGL was told to
+            expect.</para>
+        <para>Textures do not work this way. The format of an image stored in a texture is
+            controlled by OpenGL itself. The user tells it what format to use, but the specific
+            arrangements of bytes is up to OpenGL. This allows different hardware to store textures
+            in whatever way is most optimal for accessing them.</para>
+    </section>
+    <section>
+        <?dbhtml filename="Tut14 Interpolation Redux.html" ?>
+        <title>Interpolation Redux</title>
+        <para/>
+    </section>
+    <section>
+        <?dbhtml filename="Tut14 Texture Mapping.html" ?>
+        <title>Texture Mapping</title>
+        <para/>
+    </section>
+    
+    <section>
+        <?dbhtml filename="Tut14 In Review.html" ?>
+        <title>In Review</title>
+        <para>In this tutorial, you have learned the following:</para>
+        <itemizedlist>
+            <listitem>
+                <para>Textures are objects that store one or more arrays of data of some
+                    dimensionality. They can be created and filled with data from OpenGL. Shaders
+                    can reference them with sampler types, and they can access them using texturing
+                    functions.</para>
+            </listitem>
+            <listitem>
+                <para>The data in textures can represent arbitrary information. They can be used to
+                    vary a material parameter across a surface, replace a complex function with a
+                    look-up table, or anything else you might need a multi-dimensional array of
+                    values for.</para>
+            </listitem>
+            <listitem>
+                <para>Vertex or geometry shader outputs interpolated across polygons can be
+                    interpolated linearly in window space or linearly in camera space. The GLSL
+                    interpolation qualifiers control which kind of interpolation happens.</para>
+            </listitem>
+            <listitem>
+                <para>Textures can be associated with points on a surface by giving those vertex
+                    attributes texture coordinates. The texture coordinate is interpolated across
+                    the triangle's surface and then used to fetch values from a texture. This is but
+                    a part of the utility of textures.</para>
+            </listitem>
+        </itemizedlist>
+        <section>
+            <title>Further Study</title>
+            <para>Try doing these things with the given programs.</para>
+            <itemizedlist>
+                <listitem>
+                    <para>If you look at the look-up table for our specular function, you will see
+                        that much of it is very dark, if not actually at 0.0. Even when the dot
+                        product is close to 1.0, it doesn't take very far before the specular value
+                        becomes negligible. One way to improve our look-up table without having to
+                        use larger textures is to change how we index the texture. If we index the
+                        texture by the square-root of the dot-product, then there will be more room
+                        in the table for the values close to 1.0, and less for the values close to
+                        0.0. This is similar to how gamma correction works. Implement this by
+                        storing the values in the table based on the square-root of the dot-product,
+                        and then take the square-root of the dot-product in the shader before
+                        accessing the texture.</para>
+                </listitem>
+                <listitem>
+                    <para/>
+                </listitem>
+            </itemizedlist>
+        </section>
+        <section>
+            <title>Further Research</title>
+            <para/>
+        </section>
+        <section>
+            <title>OpenGL Functions of Note</title>
+            <para/>
+        </section>
+        <section>
+            <title>GLSL Functions of Note</title>
+            <para/>
+        </section>
+    </section>
+    <section>
+        <?dbhtml filename="Tut14 Glossary.html" ?>
+        <title>Glossary</title>
+        <glosslist>
+            <glossentry>
+                <glossterm>look-up table</glossterm>
+                <glossdef>
+                    <para/>
+                </glossdef>
+            </glossentry>
+            <glossentry>
+                <glossterm>texture</glossterm>
+                <glossdef>
+                    <para/>
+                </glossdef>
+            </glossentry>
+            <glossentry>
+                <glossterm>sampling</glossterm>
+                <glossdef>
+                    <para/>
+                </glossdef>
+            </glossentry>
+            <glossentry>
+                <glossterm>image</glossterm>
+                <glossdef>
+                    <para/>
+                </glossdef>
+            </glossentry>
+            <glossentry>
+                <glossterm>texture type</glossterm>
+                <glossdef>
+                    <para/>
+                </glossdef>
+            </glossentry>
+        </glosslist>
+    </section>
+</chapter>

Documents/Tutorial Documents.xpr

             <file name="Positioning/Tutorial%2007.xml"/>
             <file name="Positioning/Tutorial%2008.xml"/>
         </folder>
+        <folder name="Texturing">
+            <file name="Texturing/Tutorial%2014.xml"/>
+        </folder>
         <file name="Building%20the%20Tutorials.xml"/>
         <file name="cssDoc.txt"/>
         <file name="meshFormat.rnc"/>

Tut 14 Textures Are Not Pictures/Material Texture.cpp

 bool g_bDrawCameraPos = false;
 bool g_bDrawLights = true;
 bool g_bUseTexture = false;
-int g_currTexture = 0;
+int g_currTexture = NUM_GAUSS_TEXTURES - 1;
 
 Framework::Timer g_lightTimer = Framework::Timer(Framework::Timer::TT_LOOP, 6.0f);
 
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