implemented rect rendering using EBOs, drawing two rectangles with seperate shaders

diff --git a/gl/main.c b/gl/main.c
index 507cf58..ef5381b 100644 (file)
--- a/gl/main.c
+++ b/gl/main.c
@@ -11,58 +11,79 @@ static int screen_width = 1280;
 static int screen_height = 720;
 
 static float vertices[] = {
-       -0.5f, -0.5f, 0.0f,
-       0.5f, -0.5f, 0.0f,
-       0.0f, 0.5f, 0.0f
+       0.0f, 0.5f, 0.0f,               // top right
+       0.0f, -0.5f, 0.0f,              // bottom right
+       -1.0f, -0.5f, 0.0f,             // bottom left
+       -1.0f, 0.5f, 0.0f               // top left
 };
 
-static unsigned int vbo, vao;
-static unsigned int vertShader, fragShader, shaderProgram;
-static GLchar *vertSrc = NULL;
-static GLchar *fragSrc = NULL;
+static float vertices2[] = {
+       1.0f, 0.5f, 0.0f,               // top right
+       1.0f, -0.5f, 0.0f,              // bottom right
+       0.0f, -0.5f, 0.0f,              // bottom left
+       0.0f, 0.5f, 0.0f                // top left
+};
+
+static unsigned int indices[] = {
+       0, 1, 3,
+       1, 2, 3
+};
 
-static void initTri()
+static unsigned int ebo;
+static unsigned int vbos[2], vaos[2];
+static unsigned int vertShader[2], fragShader[2], shaderProgram[2];
+static GLchar *vertSrc[2];
+static GLchar *fragSrc[2];
+
+static void initShapes()
 {
-       glGenBuffers(1, &vbo);
-       glBindBuffer(GL_ARRAY_BUFFER, vbo);
-       glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
+       glGenBuffers(2, vbos);
+       glGenVertexArrays(2, vaos);
+       glGenBuffers(1, &ebo);
 
-       glGenVertexArrays(1, &vao);
-       glBindVertexArray(vao);
-
-       vertShader = glCreateShader(GL_VERTEX_SHADER);
-       vertSrc = shader_load_src("tri", VERTEX);
-       shader_compile(vertShader, vertSrc, "triangle vertex");
-
-       fragShader = glCreateShader(GL_FRAGMENT_SHADER);
-       fragSrc = shader_load_src("tri", FRAGMENT);
-       shader_compile(fragShader, fragSrc, "triangle fragment");
-
-       shaderProgram = glCreateProgram();
-       glAttachShader(shaderProgram, vertShader);
-       glAttachShader(shaderProgram, fragShader);
-       glLinkProgram(shaderProgram);
-
-       /*
-        * The glVertexAttribPointer call is rather complex, so I will document it
-        * here.
-        * The 1st paramater specifies the vertex attrib to configure. We want to
-        * configure the position attribute, as specified with:
-        * layout (location = 0) in tri.vert.
-        * The 2nd paramater specifies the size of the attribute to configure.
-        * We are using a vec3 value in the shader which is composed of 3 values.
-        * The 3rd specifies the data type of the paramater.
-        * The 4th specifies if the value should be normalised.
-        * The 5th specifies the size of the stride and the 6th is the offset.
-        */
+       // first shape
+       glBindVertexArray(vaos[0]);
+       glBindBuffer(GL_ARRAY_BUFFER, vbos[0]);
+       glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
        glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3*sizeof(float), (void*)0);
        glEnableVertexAttribArray(0); // param is the location of the attrib to enable.
+       glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
+       glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
+
 
-       // cleaning up
-       glDeleteShader(vertShader);
-       glDeleteShader(fragShader);
-       shader_free_src(vertSrc);
-       shader_free_src(fragSrc);
+       // second shape
+       glBindVertexArray(vaos[1]);
+       glBindBuffer(GL_ARRAY_BUFFER, vbos[1]);
+       glBufferData(GL_ARRAY_BUFFER, sizeof(vertices2), vertices2, GL_STATIC_DRAW);
+       glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3*sizeof(float), (void*)0);
+       glEnableVertexAttribArray(0);
+       glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ebo);
+       glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
+
+       glBindVertexArray(0);   // unbinding vao, since we're done
+
+       vertSrc[0] = shader_load_src("tri", VERTEX);
+       vertSrc[1] = shader_load_src("tri2", VERTEX);
+       fragSrc[0] = shader_load_src("tri", FRAGMENT);
+       fragSrc[1] = shader_load_src("tri2", FRAGMENT);
+
+       for(int i = 0; i < 2; ++i){
+               vertShader[i] = glCreateShader(GL_VERTEX_SHADER);
+               shader_compile(vertShader[i], vertSrc[i], "vertex");
+               fragShader[i] = glCreateShader(GL_FRAGMENT_SHADER);
+               shader_compile(fragShader[i], fragSrc[i], "Fragment");
+
+               shaderProgram[i] = glCreateProgram();
+               glAttachShader(shaderProgram[i], vertShader[i]);
+               glAttachShader(shaderProgram[i], fragShader[i]);
+               glLinkProgram(shaderProgram[i]);
+
+               // cleaning up
+               glDeleteShader(vertShader[i]);
+               glDeleteShader(fragShader[i]);
+               shader_free_src(vertSrc[i]);
+               shader_free_src(fragSrc[i]);
+       }
 }
 
 static bool init()
@@ -108,10 +129,15 @@ static void render()
 {
        glClearColor(0.2, 0.3, 0.3, 1.0);
        glClear(GL_COLOR_BUFFER_BIT);
+       //glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
+
+       glUseProgram(shaderProgram[0]);
+       glBindVertexArray(vaos[0]);
+       glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
 
-       glUseProgram(shaderProgram);
-       glBindVertexArray(vao);
-       glDrawArrays(GL_TRIANGLES, 0, 3);
+       glUseProgram(shaderProgram[1]);
+       glBindVertexArray(vaos[1]);
+       glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
        SDL_GL_SwapWindow(window);
 }
 
@@ -124,7 +150,7 @@ int main()
        if(!init())
                return -1;
 
-       initTri();
+       initShapes();
        itime = SDL_GetTicks();
 
 

diff --git a/gl/shaders/tri2/tri2.frag b/gl/shaders/tri2/tri2.frag
new file mode 100644 (file)
index 0000000..7eb0d06
--- /dev/null
+++ b/gl/shaders/tri2/tri2.frag
@@ -0,0 +1,7 @@
+#version 330 core
+out vec4 fragColor;
+
+void main()
+{
+       fragColor = vec4(0.2f, 0.5f, 1.0f, 1.0f);
+}

diff --git a/gl/shaders/tri2/tri2.vert b/gl/shaders/tri2/tri2.vert
new file mode 100644 (file)
index 0000000..0e6b9fc
--- /dev/null
+++ b/gl/shaders/tri2/tri2.vert
@@ -0,0 +1,7 @@
+#version 330 core
+layout (location = 0) in vec3 aPos;
+
+void main()
+{
+       gl_Position = vec4(aPos.x, aPos.y, aPos.z, 1.0);
+}