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http://anthonychan.blogbus.com/logs/28187215.html
1. An easy-forgotten problem.
When we are applying OpenGL code,we tempt to draw something without translating the coordinate. However this isnot gonna work. Because the default view point is at (0.0, 0.0, 0.0). when youtry to draw something it starts from this point and you are not gonna to seeanything
To make it different, redefinethe matrix mode:
glMatrixMode(GL_PROJECTION);
this line should be following therendering section.
Another way to do it is beforethe rendering section, define the model view:
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
gluLookAt(0.0,0.0, 1.0, 0.0, 0.0, -100.0, 0.0, 1.0, 0.0);
//just an example
2. Apiece of code making color changing
int DrawGLScene(GLvoid) // Here's Where We Do All The Drawing
{
static float r = 0.0, g = 0.0, b = 0.0;
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear Screen And Depth Buffer
glLoadIdentity(); // Reset The Current Modelview Matrix
glMatrixMode(GL_MODELVIEW); // Set the model view of the object
glLoadIdentity(); // Reset the current matrix
gluLookAt(0.0,0.0,5.0,
0.0,0.0,-100.0,
0.0,1.0,0.0); // Set the view point
if(delta < 0.0 || delta > 3.0) // In case delta is out of bound
delta = 0.0; // Reset it to zero
else if(delta < 1.0 && delta >= 0.0) // To set the red component
r = delta;
else if(delta < 2.0 && delta >= 1.0) // To set the green component
g = (delta-1.0);
else // To set the blue component
b = (delta-2.0);
delta += 0.001; // Increment the delta variable
glColor3f(r, g, b); // Set the color
glBegin(GL_TRIANGLES); // Below is the drawing of a triangle
glVertex3f(0.0, 1.0, 0.0);
glVertex3f(1.0, 0.0, 0.0);
glVertex3f(-1.0, 0.0, 0.0);
glEnd();
return TRUE; // Everything Went OK
}
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OpenGL Study Notes (2008-08-29) 2008-08-30OpenGL Study Notes (2008-08-28) 2008-08-28OpenGL Study Notes (2008-08-24) 2008-08-24OpenGL Study Notes (2008-08-16) 2008-08-19OpenGL Study Notes (2008-08-13) 2008-08-18
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