Changes between Version 48 and Version 49 of tutorial

Timestamp:

Jul 2, 2013, 11:15:31 PM (11 years ago)

Author:

leon

Comment:

Add pressure exercise

tutorial

@@ -654 +654 @@
   What happens if we don't enable temperature vertex array? Confer [attachment:temperature.c] attached if having troubles.
  3. Add additional custom vertex array for the pressure. Change the temperature array to have values in Celsius for water boiling range [0-100]°C. Pressure should be in the range of [0-1] MPa. Scaling to color range [0-1] should be done in shaders. Toggle between them with the keyboard event by using the keys `'p'` and `'t`' that {{{glEnableVertexAttribArray()}}} and {{{glDisableVertexAttribArray()}}} corresponding vertex attribute arrays.
-
+ 4. [[Image(pressure.png,right)]] Fetch pressure data as 2D y-slice in file [attachment:p_yNormal.vtk] formatted in [http://www.vtk.org VTK] that can be quickly read by the following code:
+{{{
+#!c
+GLfloat *point;   int points;
+GLuint *triangle; int triangles;
+GLfloat *pressure;  
+
+void read_VTK_pressure(const char *filename)
+{
+  char line[80];
+  int i; FILE *f;
+  f = fopen(filename, "r"); 
+  while(fgets(line, 80, f))
+    {
+      if (strstr(line, "POINTS"))
+        {
+          float dummy_y;
+          points = atof(line+7);
+          point = malloc(points*2*sizeof(float));
+          pressure = malloc(points*sizeof(float));
+          assert(point != NULL && pressure != NULL);
+          for(i = 0; i < points; ++i)
+            fscanf(f, "%f %f %f", &point[i*2], &dummy_y, &point[i*2+1]);
+        }
+      else if (strstr(line, "POLYGONS"))
+        {
+          triangles = atof(line+9);
+          triangle = malloc(triangles*3*sizeof(GLuint));
+          for (i = 0; i < triangles; ++i)
+            {
+              int n;
+              fscanf(f, "%d %d %d %d", &n, &triangle[i*3],
+                     &triangle[i*3+1], &triangle[i*3+2]);
+            }
+        }
+      else if (strstr(line, "FIELD"))
+        {
+          fgets(line, 80, f); // skip: p 1 27582 float
+          for (i = 0; i < points; ++i)
+            fscanf(f, "%f", &pressure[i]);
+        }
+    }
+  fclose(f);
+  printf("Read %d points for %d triangles for field %s\n",
+         points, triangles, filename);
+}
+}}}
+ Insert this code into [attachment:temperature.c] and rename temperature with pressure   everywhere. We will be drawing indexed so the last lines of the {{{display()}} reads
+{{{
+#!c
+  glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo_elements);
+  glDrawElements(GL_TRIANGLES, triangles*3, GL_UNSIGNED_INT, 0);
+  glutSwapBuffers();
+}}}
+ Sending element data buffers to GPU is slightly changed by using  {{{GL_ELEMENT_ARRAY_BUFFER}}} instead of {{{GL_ARRAY_BUFFER}}} in subroutine
+{{{
+#!c
+void send_buffers_to_GPU(void)
+{
+  GLuint vertex_array_object;
+  glGenVertexArrays(1, &vertex_array_object);
+  glBindVertexArray(vertex_array_object);
+  
+  glGenBuffers(1, &vbo_vertices);
+  glBindBuffer(GL_ARRAY_BUFFER, vbo_vertices);
+  glBufferData(GL_ARRAY_BUFFER, points*2*sizeof(GLfloat), point, GL_STATIC_DRAW);
+
+  glGenBuffers(1, &vbo_pressure);
+  glBindBuffer(GL_ARRAY_BUFFER, vbo_pressure);
+  glBufferData(GL_ARRAY_BUFFER, points*sizeof(GLfloat), pressure, GL_STATIC_DRAW);
+
+  glGenBuffers(1, &ibo_elements);
+  glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, ibo_elements);
+  glBufferData(GL_ELEMENT_ARRAY_BUFFER, triangles*3*sizeof(GLuint),
+               triangle, GL_STATIC_DRAW);
+}
+}}}
+ Positioning (translation) of the motorbike and scaling of the pressure [-300..200] to color mix range [0-1] can be done in shaders directly. Confer final [attachment:pressure.c] if having trubles with coding.
 
 == Interactivity ==
@@ -1052 +1129 @@
  1. Draw streamlines with velocity colorization
  1. Convert example into GPU buffered (VBOs). 
+ 1. Combine sliced pressure data(VTK) and model (OBJ) together as custom CFD visualization not available in visualization tools to date.