report.latex

   1 \documentclass{article}
   2 \usepackage{fullpage}
   3 \usepackage{listings}
   4 \usepackage{graphicx}
   5 \begin{document}
   6
   7 \author{Luke Lau}
   8 \title{CS4052 Assignment 1}
   9 \maketitle
  10
  11 \lstset{basicstyle=\ttfamily}
  12
  13 \section{Fragment shader colours}
  14 In order to get the fragment shader to use the position as the colour,
  15 I had to add an input \texttt{vec4} for the \texttt{vec4 color} that the vertex shader
  16 outputted. Since the inputs to the fragment shader are from the vertex shader, I had to
  17 use \texttt{color} and not \texttt{vColor}.
  18 \lstinputlisting[language=C++]{fragment.glsl}
  19 \begin{center}
  20         \includegraphics[width=0.8\textwidth]{part1}
  21 \end{center}
  22
  23
  24 \section{Two triangles}
  25
  26 Two add two triangles, I had to increase the number of vertices drawn to 6
  27
  28 \begin{lstlisting}[language=C++]
  29 glDrawArrays(GL_TRIANGLES, 0, 6);
  30 \end{lstlisting}
  31
  32 And add 9 new coordinates and colours for them.
  33
  34 \begin{lstlisting}[language=C++]
  35 GLfloat vertices[] = {
  36         0.0f, -1.0f, 0.0f,
  37         1.0f, -1.0f, 0.0f,
  38         0.5f, 1.0f, 0.0f,
  39         -1.0f, -1.0f, 0.0f,
  40         0.0f, -1.0f, 0.0f,
  41         -0.5f, 1.0f, 0.0f
  42 }
  43 GLfloat colors[] = {
  44         0, 1, 0, 1,
  45         1, 0, 0, 1,
  46         0, 0, 1, 1,
  47         0, 1, 0, 1,
  48         1, 0, 0, 1,
  49         0, 0, 1, 1
  50 };
  51 \end{lstlisting}
  52
  53 \begin{center}
  54         \includegraphics[width=0.8\textwidth]{part2}
  55 \end{center}
  56
  57
  58 \section{Two triangles, two VAOs and two VBOs}
  59
  60 In order to use two VAOs and two VBOs, I had to combine the VAO setup and the VBO setup
  61 into one function, since you need to bind the VBO at the time that you create the
  62 corresponding VAO.
  63
  64 \begin{lstlisting}[language=C++]
  65 #define BUFFER_OFFSET(i) ((char *)NULL + (i))
  66
  67 GLuint setupBuffers(GLfloat* vertices, GLuint progId) {
  68
  69         GLfloat colors[] = {
  70                 0, 1, 0, 1,
  71                 1, 0, 0, 1,
  72                 0, 0, 1, 1
  73         };
  74
  75         GLuint numVerts = 3;
  76
  77         GLuint vbo;
  78         glGenBuffers(1, &vbo);
  79
  80         GLuint vao;
  81         glGenVertexArrays(1, &vao);
  82
  83         GLuint posId = glGetAttribLocation(progId, "vPosition");
  84         GLuint colorId = glGetAttribLocation(progId, "vColor");
  85
  86         GLuint vertsLen = numVerts * 3 * sizeof(GLfloat);
  87         GLuint colorsLen = numVerts * 4 * sizeof(GLfloat);
  88
  89         glBindBuffer(GL_ARRAY_BUFFER, vbo);
  90         glBufferData(GL_ARRAY_BUFFER, vertsLen + colorsLen, NULL, GL_STATIC_DRAW);
  91
  92         glBufferSubData(GL_ARRAY_BUFFER, 0, vertsLen, vertices);
  93         glBufferSubData(GL_ARRAY_BUFFER, vertsLen, colorsLen, colors);
  94
  95         glBindVertexArray(vao);
  96
  97         glEnableVertexAttribArray(posId);
  98         glEnableVertexAttribArray(colorId);
  99
 100         glVertexAttribPointer(posId, 3, GL_FLOAT, GL_FALSE, 0, 0);
 101         glVertexAttribPointer(colorId, 4, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(numVerts * 3 * sizeof(GLfloat)));
 102
 103         return vao;
 104 }
 105 \end{lstlisting}
 106
 107 This could then be used like so:
 108 \begin{lstlisting}[language=C++]
 109 GLfloat vertices[2][9] = {
 110         {
 111                 0.0f, -1.0f, 0.0f,
 112                 1.0f, -1.0f, 0.0f,
 113                 0.5f, 1.0f, 0.0f
 114         },
 115
 116         {
 117                 -1.0f, -1.0f, 0.0f,
 118                 0.0f, -1.0f, 0.0f,
 119                 -0.5f, 1.0f, 0.0f
 120         }
 121 };
 122 GLuint* vaos = new GLuint[2];
 123 vaos[0] = setupBuffers(vertices[0], progId);
 124 vaos[1] = setupBuffers(vertices[1], progId);
 125 \end{lstlisting}
 126
 127 When drawing, the VAOs needed to be switched out:
 128
 129 \begin{lstlisting}[language=C++]
 130 void display() {
 131         glClear(GL_COLOR_BUFFER_BIT);
 132         for (int i = 0; i < 2; i++) {
 133                 glBindVertexArray(vaos[i]);
 134                 glDrawArrays(GL_TRIANGLES, 0, 3);
 135         }
 136         glutSwapBuffers();
 137 }
 138 \end{lstlisting}
 139
 140 \section{Two separate shaders}
 141
 142 I modified the \texttt{compileShaders} function to load in the shader source from a file:
 143 \begin{lstlisting}[language=C++]
 144 GLuint compileShaders(char* vertexShader, char* fragmentShader) {
 145         GLuint progId = glCreateProgram();
 146
 147         attachShader(progId, vertexShader, GL_VERTEX_SHADER);
 148         attachShader(progId, fragmentShader, GL_FRAGMENT_SHADER);
 149
 150         glLinkProgram(progId);
 151         GLint success = 0;
 152         glGetProgramiv(progId, GL_LINK_STATUS, &success);
 153         if (!success) {
 154                 GLchar log[1024];
 155                 glGetProgramInfoLog(progId, sizeof(log), NULL, log);
 156                 fprintf(stderr, "error linking: %s\n", log);
 157                 exit(1);
 158         }
 159
 160         return progId;
 161 }
 162 \end{lstlisting}
 163
 164 Which meant I could easily swap out the programs used when setting up the buffers:
 165
 166 \begin{lstlisting}[language=C++]
 167 progIds = new GLuint[2];
 168
 169 GLuint progId1 = compileShaders((char*)"vertex.glsl", (char*)"fragment.glsl");
 170 vaos[0] = setupBuffers(vertices[0], progId1);
 171 progIds[0] = progId1;
 172 validateProgram(progId1);
 173
 174 GLuint progId2 = compileShaders((char*)"vertex.glsl", (char*)"yellow.glsl");
 175 vaos[1] = setupBuffers(vertices[1], progId2);
 176 progIds[1] = progId2;
 177 validateProgram(progId2);
 178 \end{lstlisting}
 179
 180 The new yellow shader looked like this:
 181
 182 \lstinputlisting[language=C++]{yellow.glsl}
 183
 184 I needed to switch programs during the display function:
 185
 186 \begin{lstlisting}[language=C++]
 187 void display() {
 188         glClear(GL_COLOR_BUFFER_BIT);
 189         for (int i = 0; i < 2; i++) {
 190                 glUseProgram(progIds[i]);
 191                 glBindVertexArray(vaos[i]);
 192                 glDrawArrays(GL_TRIANGLES, 0, 3);
 193         }
 194         glutSwapBuffers();
 195 }
 196 \end{lstlisting}
 197
 198 \begin{center}
 199         \includegraphics[width=0.8\textwidth]{part4}
 200 \end{center}
 201
 202
 203 \end{document}