better test of point attenuation

diff --git a/progs/trivial/point-param.c b/progs/trivial/point-param.c
index 520bca9ea2d621dc373b6108e2fcccf52f6cc5e5..02500cd34e885878b6a0fbe77b9c19af260a64e6 100644 (file)
--- a/progs/trivial/point-param.c
+++ b/progs/trivial/point-param.c
@@ -23,15 +23,13 @@
  */
 
 #define GL_GLEXT_PROTOTYPES
+#include <math.h>
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
 #include <GL/glut.h>
 
 
-#define CI_OFFSET_1 16
-#define CI_OFFSET_2 32
-
 
 GLenum doubleBuffer;
 
@@ -41,53 +39,63 @@ static void Init(void)
    fprintf(stderr, "GL_VERSION    = %s\n", (char *) glGetString(GL_VERSION));
    fprintf(stderr, "GL_VENDOR     = %s\n", (char *) glGetString(GL_VENDOR));
 
-    glClearColor(0.0, 0.0, 1.0, 0.0);
+   glClearColor(0.0, 0.0, 1.0, 0.0);
 }
 
 static void Reshape(int width, int height)
 {
-
     glViewport(0, 0, (GLint)width, (GLint)height);
 
     glMatrixMode(GL_PROJECTION);
     glLoadIdentity();
-    glOrtho(-1.0, 1.0, -1.0, 1.0, -0.5, 1000.0);
+    glOrtho(-1.0, 1.0, -1.0, 1.0, 0, 100.0);
     glMatrixMode(GL_MODELVIEW);
 }
 
 static void Key(unsigned char key, int x, int y)
 {
-
     switch (key) {
-      case 27:
+    case 27:
        exit(1);
-      default:
+    default:
        return;
     }
-
     glutPostRedisplay();
 }
 
+
+static float
+expected(float z, float size, const float atten[3])
+{
+   float dist = fabs(z);
+   const GLfloat q = atten[0] + dist * (atten[1] + dist * atten[2]);
+   const GLfloat a = sqrt(1.0 / q);
+   return size * a;
+}
+
+
 static void Draw(void)
 {
-   static GLfloat theQuad[3] = { 0.25, 0.0, 1/60.0 };
+   static GLfloat atten[3] = { 0.0, 0.1, .01 };
+   float size = 40.0;
+   int i;
 
    glClear(GL_COLOR_BUFFER_BIT); 
 
    glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
-   glPointSize(8.0);
-   glPointParameterfvARB(GL_POINT_DISTANCE_ATTENUATION_ARB, theQuad); 
+   glPointSize(size);
+   glPointParameterfvARB(GL_POINT_DISTANCE_ATTENUATION_ARB, atten); 
 
+   glColor3f(1,0,0); 
 
+   printf("Expected point sizes:\n");
    glBegin(GL_POINTS);
-   glColor3f(1,0,0); 
-   glVertex3f( 0.9, -0.9, -30.0);
-   glColor3f(1,1,0); 
-   glVertex3f( 0.9,  0.9, -30.0);
-   glColor3f(1,0,1); 
-   glVertex3f(-0.9,  0.9, -30.0);
-   glColor3f(0,1,1); 
-   glVertex3f(-0.9,  -0.9, -30.0);
+   for (i = 0; i < 5; i++) {
+      float x = -0.8 + i * 0.4;
+      float z = -i * 20 - 10;
+      glVertex3f( x, 0.0, z);
+      printf(" %f\n", expected(z, size, atten));
+   }
    glEnd();
 
    glFlush();
@@ -97,6 +105,7 @@ static void Draw(void)
    }
 }
 
+
 static GLenum Args(int argc, char **argv)
 {
     GLint i;
@@ -116,6 +125,7 @@ static GLenum Args(int argc, char **argv)
     return GL_TRUE;
 }
 
+
 int main(int argc, char **argv)
 {
     GLenum type;
@@ -132,7 +142,7 @@ int main(int argc, char **argv)
     type |= (doubleBuffer) ? GLUT_DOUBLE : GLUT_SINGLE;
     glutInitDisplayMode(type);
 
-    if (glutCreateWindow("First Tri") == GL_FALSE) {
+    if (glutCreateWindow(argv[0]) == GL_FALSE) {
        exit(1);
     }
 
@@ -142,5 +152,5 @@ int main(int argc, char **argv)
     glutKeyboardFunc(Key);
     glutDisplayFunc(Draw);
     glutMainLoop();
-       return 0;
+    return 0;
 }