Changes between Version 36 and Version 37 of tutorial

Timestamp:

Jun 30, 2013, 9:32:00 PM (12 years ago)

Author:

leon

Comment:

Fix temperature example

tutorial

@@ -159 +159 @@
 Create {{{triangle.c}}} and update {{{Makefile}}} with new target 
 {{{
-#!sh
+#!c
 #include <stdio.h>
 #include <stdlib.h>
@@ -165 +165 @@
 #include <GL/glut.h>
 
-static const GLchar * vertex_shader[] =
-  {"void main()"
-   "{"
-   "  gl_Position = ftransform();"
-   "}"
-  };
+GLuint program;
+GLuint vbo_vertices;
+GLint attribute_coord2d;
+
+static const GLchar * vertex_shader[] = {
+  "attribute vec2 coord2d;" // input vertex position
+  "void main()"
+  "{"
+  "  gl_Position = gl_ModelViewProjectionMatrix*vec4(coord2d, 0.0, 1.0);"
+  "}"
+};
 static const GLchar * fragment_shader[] =
   {"void main()"
@@ -178 +183 @@
   };
 
-void setShaders()
-{
-  GLuint v, f, p;
+void create_shaders()
+{
+  GLuint v, f;
 
   v = glCreateShader(GL_VERTEX_SHADER);
@@ -188 +193 @@
   glCompileShader(v);
   glCompileShader(f);
-  p = glCreateProgram();
-  glAttachShader(p,f);
-  glAttachShader(p,v);
-  glLinkProgram(p);
-  glUseProgram(p);
-}
-
-
-enum VAO_IDs { Triangles, NumVAOs };
-enum Buffer_IDs {ArrayBuffer,NumBuffers};
-enum Attrib_IDs { vPosition = 0 };
-GLuint VAOs[NumVAOs];
-GLuint Buffers[NumBuffers];
-#define NumVertices  6 
-
-void init(void) 
-{
-  glGenVertexArrays(NumVAOs, VAOs);
-  glBindVertexArray(VAOs[Triangles]);
-  GLfloat vertices[NumVertices][2] = {
+  program = glCreateProgram();
+  glAttachShader(program, f);
+  glAttachShader(program, v);
+  glLinkProgram(program);
+  glUseProgram(program);
+
+  attribute_coord2d = glGetAttribLocation(program, "coord2d");
+  if (attribute_coord2d == -1) {
+    fprintf(stderr, "Could not bind attribute coord2d\n");
+  }
+  glEnableVertexAttribArray(attribute_coord2d);
+}
+
+void send_buffers_to_GPU(void)
+{
+  GLuint vertex_array_object;
+  glGenVertexArrays(1, &vertex_array_object);
+  glBindVertexArray(vertex_array_object);
+  
+  GLfloat vertices[][2] = {
     { -0.90, -0.90 }, // Triangle 1
     {  0.85, -0.90 },
@@ -215 +220 @@
     { -0.85,  0.90 }
   };
-  glGenBuffers(NumBuffers, Buffers);
-  glBindBuffer( GL_ARRAY_BUFFER, Buffers[ArrayBuffer]);
+
+  glGenBuffers(1, &vbo_vertices);
+  glBindBuffer( GL_ARRAY_BUFFER, vbo_vertices);
   glBufferData( GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
-  glVertexAttribPointer(vPosition, 2, GL_FLOAT, GL_FALSE, 0, (const void*)0);
-  glEnableVertexAttribArray(vPosition);
 }
 
@@ -226 +230 @@
 {
   glClear(GL_COLOR_BUFFER_BIT);
-  glBindVertexArray(VAOs[Triangles]);
-  glDrawArrays(GL_TRIANGLES, 0, NumVertices);
+  glBindBuffer(GL_ARRAY_BUFFER, vbo_vertices);
+  glVertexAttribPointer(attribute_coord2d, 2, GL_FLOAT, GL_FALSE, 0, NULL);
+  glDrawArrays(GL_TRIANGLES, 0, 6); // Draw 6 vertices
   glutSwapBuffers();
 }
@@ -244 +249 @@
    }
   glClearColor(0.9,1.0,1.0,1.0);
-  init();
-  setShaders();
+  send_buffers_to_GPU();
+  create_shaders();
   glutMainLoop();
-  return 0;
+  return EXIT_SUCCESS;
 }
 }}}
 [[Image(triangle.png,align=bottom,right,title=Triangles )]]
 === Exercises #2 ===
- 1. To be able to continue and not get lost introduce shader compiler logs in case of compilation errors by adding the following code into {{{setShaders()}}} right at after vertex shader compilation:
-   {{{
-   #!c
-    GLint compiled;
-    glGetShaderiv(v, GL_COMPILE_STATUS, &compiled );
-    if ( !compiled ) {
-      GLsizei len;
-      glGetShaderiv( v, GL_INFO_LOG_LENGTH, &len );
-      GLchar* log = malloc(sizeof(GLchar)*(len+1));
-      printf("Vertex Shader compilation failed: %s\n", log);
-      free(log);
-    }
-   }}}
+ 1. To be able to continue and not get lost introduce shader compiler logs in case of compilation errors by adding the following code into {{{create_shaders()}}} right at after vertex shader compilation:
+  {{{
+  #!c
+  GLint compiled;
+  glGetShaderiv(v, GL_COMPILE_STATUS, &compiled );
+  if ( !compiled ) {
+    GLsizei  maxLength, length;
+    glGetShaderiv( v, GL_INFO_LOG_LENGTH, &maxLength );
+    GLchar* log = malloc(sizeof(GLchar)*(maxLength+1));
+    glGetShaderInfoLog(v,  maxLength, &length, log);
+    printf("Vertex Shader compilation failed: %s\n", log);
+    free(log);
+  }
+  }}}
  Do not forget to repeat the same thing for fragment shader.
  Add linker debugging
-   {{{
-   #!c  
-    GLint linked;
-    glGetProgramiv(p, GL_LINK_STATUS, &linked );
-    if ( !linked ) {
-      GLsizei len;
-      glGetProgramiv( p, GL_INFO_LOG_LENGTH, &len );
-      GLchar* log = malloc(sizeof(GLchar)*(len+1));
-      glGetProgramInfoLog( p, len, &len, log );
-      printf("Shader linking failed: %s\n", log);
-      free(log);
-    }
-   }}}
-   Create some error to verify if it works.
+  {{{
+  #!c  
+  GLint linked;
+  glGetProgramiv(program, GL_LINK_STATUS, &linked );
+  if ( !linked ) {
+    GLsizei len;
+    glGetProgramiv(program, GL_INFO_LOG_LENGTH, &len );
+    GLchar* log = malloc(sizeof(GLchar)*(len+1));
+    glGetProgramInfoLog(program, len, &len, log );
+    printf("Shader linking failed: %s\n", log);
+    free(log);
+  }
+  }}}
+  Create some error to verify if it works.
   For general (core) OpenGL errors we can use the following `glcheck()` utility at suspicious places.
   {{{
@@ -288 +294 @@
                            gluErrorString(s),  __LINE__);}
   }}}
- 2. Introduce vertex temperature with additional array and buffer at the end off `init()`
-  [[Image(temperature.png,right)]]
+ 2. [[Image(temperature.png,right)]] Copy `triangle.c` into `temperature.c` and introduce vertex temperature with additional array and buffer at the end of `send_buffers_to_GPU()` 
   {{{
   #!c
   GLfloat vertex_temperature[] = {0, 1, 0.2, 0.1, 0.5, 0.9};
-  glBindBuffer(GL_ARRAY_BUFFER, Buffers[TempBuffer]);
+  glGenBuffers(1, &vbo_temperature);
+  glBindBuffer(GL_ARRAY_BUFFER, vbo_temperature);
   glBufferData(GL_ARRAY_BUFFER, sizeof(vertex_temperature),
-               vertex_temperature, GL_STATIC_DRAW);
-  glVertexAttribPointer(tPosition, 1, GL_FLOAT, GL_FALSE, 0, NULL);
-  glEnableVertexAttribArray(tPosition);//toggle this
-  }}}
-  and adding corresponding IDs to `VAOs` and buffers. Replace shaders with
+             vertex_temperature, GL_STATIC_DRAW);
+  }}}
+  and adding corresponding global attribute and VBOs IDs at the top of `temperature.c` so that global section reads:   
+  {{{
+  #!c
+  GLuint program;
+  GLuint vbo_vertices;
+  GLUINT vbo_temperature;
+  GLint attribute_coord2d;
+  GLint attribute_temperature;
+ }}}  
+ Replace shaders with
   {{{
   #!c
@@ -322 +335 @@
   "}"
 };
+  }}}
+  Bind temperature buffer and specify data layout within {{{display()}}} just before {{{glDrawElements()}}} with
+  {{{
+  #!c
+  glBindBuffer(GL_ARRAY_BUFFER, vbo_temperature);
+  glVertexAttribPointer(attribute_temperature, 1, GL_FLOAT, GL_FALSE, 0, NULL);
   }}}
   What happens if we don't enable temperature vertex array? Confer [attachment:temperature.c] attached if having troubles.