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Asked: 2026-05-11T06:38:41+00:00

This is probably a silly mistake but I cant see it?! I have classes

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This is probably a silly mistake but I cant see it?! I have classes defining geometry and classes that render that geometry. Right now it is basic triangles and colours for each vertex.

Here is the code defining said geometry objects data:

CGeometry* g = new CGeometry(); g->vertexes = new double[3*3];  g->vertexes[0] = 0; g->vertexes[1] = 0; g->vertexes[2] = 0;  g->vertexes[3] = 100; g->vertexes[4] = 100; g->vertexes[5] = 0;  g->vertexes[6] = 100; g->vertexes[7] = 0; g->vertexes[8] = 0;  g->colors = new double[12];  g->colors[0] = 1; g->colors[1] = 1; g->colors[2] = 0; g->colors[3] = 1;  g->colors[4] = 1; g->colors[5] = 0; g->colors[6] = 1; g->colors[7] = 0;  g->colors[8] = 0; g->colors[9] = 1; g->colors[10] = 1; g->colors[11] = 0;

And here is the code that renders said data:

CGeometry* g = object->geometry;  int j = object->endIndex - object->startIndex; double* vertexes = g->vertexes; double* colors = g->colors;  glBegin(GL_TRIANGLES); {     for(int i = 0; i < j; i++){         int coord = object->startIndex+i;         int colorind = coord*4;          double r,g,b,a;         r = colors[colorind];         g = colors[colorind+1];         b = colors[colorind+2];         a = colors[colorind+3];          glColor4d(  r,g,b,a);         glVertex3d( vertexes[coord*3],                     vertexes[coord*3+1],                     vertexes[coord*3+2]);     } } glEnd();

Yet regardless of what I put my triangle is always yellow, or the value of the first color in the colors array. I have gone into the debugger and checked the values on each individual loop iteration and the values of the r g b and a variables do infact change accordingly and are not always yellow, yet the result is a yellow triangle.

Yet if I put the following nabbed from the neheGL tutorials:

glClearColor(0.1f,0.1f,0.1f,1); glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear Screen And Depth Buffer glLoadIdentity();                                   // Reset The Current Modelview Matrix //glTranslatef(1.5f,0.0f,0.0f);                     // Move Left 1.5 Units And Into The Screen 6.0 glBegin(GL_TRIANGLES);                              // Drawing Using Triangles     glColor3f(1.0f,0.0f,0.0f);                      // Set The Color To Red     glVertex3f( 0.0f, 1.0f, 0.0f);                  // Top     glColor3f(0.0f,1.0f,0.0f);                      // Set The Color To Green     glVertex3f(-1.0f,-1.0f, 0.0f);                  // Bottom Left     glColor3f(0.0f,0.0f,1.0f);                      // Set The Color To Blue     glVertex3f( 1.0f,-1.0f, 0.0f);                  // Bottom Right glEnd();                                            // Finished Drawing The Triangle glTranslatef(160.0f,0.0f,0.0f);                     // Move Right 3 Units glColor3f(0.5f,0.5f,1.0f);                          // Set The Color To Blue One Time Only glBegin(GL_QUADS);                                  // Draw A Quad     glVertex3f(-1.0f, 1.0f, 0.0f);                  // Top Left     glVertex3f( 1.0f, 1.0f, 0.0f);                  // Top Right     glVertex3f( 1.0f,-1.0f, 0.0f);                  // Bottom Right     glVertex3f(-1.0f,-1.0f, 0.0f);                  // Bottom Left glEnd();

I get a nice blended triangle with 3 colours from each vertex

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1 Answer

  1. Actually, I think I got it: you’re only seeing a small portion of the bottom left corner of your triangle. You need to move away from it to view it entirely: your coordinates are too large.

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