X-Git-Url: https://git.lukelau.me/?p=opengl.git;a=blobdiff_plain;f=assignment-1%2Freport.latex;fp=assignment-1%2Freport.latex;h=3193a7e306da9f61834cb9afff161fbd04293e5a;hp=0000000000000000000000000000000000000000;hb=150ba29f1ce70777762cb7fc44e00e52339bb66e;hpb=5fa27af6222eab1f43e6ca01f1c37cbfa1d86fcd

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+\documentclass{article}
+\usepackage{fullpage}
+\usepackage{listings}
+\usepackage{graphicx}
+\begin{document}
+
+\author{Luke Lau}
+\title{CS4052 Assignment 1}
+\maketitle
+
+\lstset{basicstyle=\ttfamily}
+
+\section{Fragment shader colours}
+In order to get the fragment shader to use the position as the colour,
+I had to add an input \texttt{vec4} for the \texttt{vec4 color} that the vertex shader
+outputted. Since the inputs to the fragment shader are from the vertex shader, I had to
+use \texttt{color} and not \texttt{vColor}.
+\lstinputlisting[language=C++]{fragment.glsl}
+\begin{center}
+	\includegraphics[width=0.8\textwidth]{part1}
+\end{center}
+
+
+\section{Two triangles}
+
+Two add two triangles, I had to increase the number of vertices drawn to 6
+
+\begin{lstlisting}[language=C++]
+glDrawArrays(GL_TRIANGLES, 0, 6);
+\end{lstlisting}
+
+And add 9 new coordinates and colours for them.
+
+\begin{lstlisting}[language=C++]
+GLfloat vertices[] = {
+	0.0f, -1.0f, 0.0f,
+	1.0f, -1.0f, 0.0f,
+	0.5f, 1.0f, 0.0f,
+	-1.0f, -1.0f, 0.0f,
+	0.0f, -1.0f, 0.0f,
+	-0.5f, 1.0f, 0.0f
+}
+GLfloat colors[] = {
+	0, 1, 0, 1,
+	1, 0, 0, 1,
+	0, 0, 1, 1,
+	0, 1, 0, 1,
+	1, 0, 0, 1,
+	0, 0, 1, 1		
+};
+\end{lstlisting}
+
+\begin{center}
+	\includegraphics[width=0.8\textwidth]{part2}
+\end{center}
+
+
+\section{Two triangles, two VAOs and two VBOs}
+
+In order to use two VAOs and two VBOs, I had to combine the VAO setup and the VBO setup
+into one function, since you need to bind the VBO at the time that you create the 
+corresponding VAO.
+
+\begin{lstlisting}[language=C++]
+#define BUFFER_OFFSET(i) ((char *)NULL + (i))
+
+GLuint setupBuffers(GLfloat* vertices, GLuint progId) {
+
+	GLfloat colors[] = {
+		0, 1, 0, 1,
+		1, 0, 0, 1,
+		0, 0, 1, 1
+	};
+
+	GLuint numVerts = 3;
+
+	GLuint vbo;
+	glGenBuffers(1, &vbo);
+
+	GLuint vao;
+	glGenVertexArrays(1, &vao);
+
+	GLuint posId = glGetAttribLocation(progId, "vPosition");
+	GLuint colorId = glGetAttribLocation(progId, "vColor");
+
+	GLuint vertsLen = numVerts * 3 * sizeof(GLfloat);
+	GLuint colorsLen = numVerts * 4 * sizeof(GLfloat);
+
+	glBindBuffer(GL_ARRAY_BUFFER, vbo);
+	glBufferData(GL_ARRAY_BUFFER, vertsLen + colorsLen, NULL, GL_STATIC_DRAW);
+
+	glBufferSubData(GL_ARRAY_BUFFER, 0, vertsLen, vertices);
+	glBufferSubData(GL_ARRAY_BUFFER, vertsLen, colorsLen, colors);
+	
+	glBindVertexArray(vao);
+
+	glEnableVertexAttribArray(posId);
+	glEnableVertexAttribArray(colorId);
+	
+	glVertexAttribPointer(posId, 3, GL_FLOAT, GL_FALSE, 0, 0);
+	glVertexAttribPointer(colorId, 4, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(numVerts * 3 * sizeof(GLfloat)));
+
+	return vao;
+}
+\end{lstlisting}
+
+This could then be used like so:
+\begin{lstlisting}[language=C++]
+GLfloat vertices[2][9] = {
+	{
+		0.0f, -1.0f, 0.0f,
+		1.0f, -1.0f, 0.0f,
+		0.5f, 1.0f, 0.0f
+	},
+
+	{
+		-1.0f, -1.0f, 0.0f,
+		0.0f, -1.0f, 0.0f,
+		-0.5f, 1.0f, 0.0f
+	}
+};
+GLuint* vaos = new GLuint[2];
+vaos[0] = setupBuffers(vertices[0], progId);
+vaos[1] = setupBuffers(vertices[1], progId);
+\end{lstlisting}
+
+When drawing, the VAOs needed to be switched out:
+
+\begin{lstlisting}[language=C++]
+void display() {
+	glClear(GL_COLOR_BUFFER_BIT);
+	for (int i = 0; i < 2; i++) {
+		glBindVertexArray(vaos[i]);
+		glDrawArrays(GL_TRIANGLES, 0, 3);
+	}
+	glutSwapBuffers();
+}
+\end{lstlisting}
+
+\section{Two separate shaders}
+
+I modified the \texttt{compileShaders} function to load in the shader source from a file:
+\begin{lstlisting}[language=C++]
+GLuint compileShaders(char* vertexShader, char* fragmentShader) {
+	GLuint progId = glCreateProgram();
+
+	attachShader(progId, vertexShader, GL_VERTEX_SHADER);
+	attachShader(progId, fragmentShader, GL_FRAGMENT_SHADER);
+
+	glLinkProgram(progId);
+	GLint success = 0;
+	glGetProgramiv(progId, GL_LINK_STATUS, &success);
+	if (!success) {
+		GLchar log[1024];
+		glGetProgramInfoLog(progId, sizeof(log), NULL, log);
+		fprintf(stderr, "error linking: %s\n", log);
+		exit(1);
+	}
+
+	return progId;
+}
+\end{lstlisting}
+
+Which meant I could easily swap out the programs used when setting up the buffers:
+
+\begin{lstlisting}[language=C++]
+progIds = new GLuint[2];
+
+GLuint progId1 = compileShaders((char*)"vertex.glsl", (char*)"fragment.glsl");
+vaos[0] = setupBuffers(vertices[0], progId1);
+progIds[0] = progId1;
+validateProgram(progId1);
+
+GLuint progId2 = compileShaders((char*)"vertex.glsl", (char*)"yellow.glsl");
+vaos[1] = setupBuffers(vertices[1], progId2);
+progIds[1] = progId2;
+validateProgram(progId2);
+\end{lstlisting}
+
+The new yellow shader looked like this:
+
+\lstinputlisting[language=C++]{yellow.glsl}
+
+I needed to switch programs during the display function:
+
+\begin{lstlisting}[language=C++]
+void display() {
+	glClear(GL_COLOR_BUFFER_BIT);
+	for (int i = 0; i < 2; i++) {
+		glUseProgram(progIds[i]);
+		glBindVertexArray(vaos[i]);
+		glDrawArrays(GL_TRIANGLES, 0, 3);
+	}
+	glutSwapBuffers();
+}
+\end{lstlisting}
+
+\begin{center}
+	\includegraphics[width=0.8\textwidth]{part4}
+\end{center}
+
+
+\end{document}