Читать онлайн "NeHe's OpenGL Tutorials" - Christopoulos Dimitrios - RuLit

In this tutorial I'll teach you how to use three different texture filters. I'll teach you how to move an object using keys on the keyboard, and I'll also teach you how to apply simple lighting to your OpenGL scene. Lots covered in this tutorial, so if the previous tutorials are giving you problems, go back and review. It's important to have a good understanding of the basics before you jump into the following code.

We're going to be modifying the code from lesson one again. As usual, if there are any major changes, I will write out the entire section of code that has been modified. We'll start off by adding a few new variables to the program.

#include <windows.h> // Header File For Windows

#include <stdio.h> // Header File For Standard Input/Output ( ADD )

#include <gl\gl.h> // Header File For The OpenGL32 Library

#include <gl\glu.h> // Header File For The GLu32 Library

#include <gl\glaux.h> // Header File For The GLaux Library

HDC hDC=NULL; // Private GDI Device Context HGLRC

hRC=NULL; // Permanent Rendering Context

HWND hWnd=NULL; // Holds Our Window Handle

HINSTANCE hInstance; // Holds The Instance Of The Application

bool keys[256]; // Array Used For The Keyboard Routine

bool active=TRUE; // Window Active Flag

bool fullscreen=TRUE; // Fullscreen Flag

The lines below are new. We're going to add three boolean variables. BOOL means the variable can only be TRUE or FALSE. We create a variable called light to keep track of whether or not the lighting is on or off. The variables lp and fp are used to store whether or not the 'L' or 'F' key has been pressed. I'll explain why we need these variables later on in the code. For now, just know that they are important.

BOOL light; // Lighting ON / OFF

BOOL lp; // L Pressed?

BOOL fp; // F Pressed?

Now we're going to set up five variables that will control the angle on the x axis (xrot), the angle on the y axis (yrot), the speed the crate is spinning at on the x axis (xspeed), and the speed the crate is spinning at on the y axis (yspeed). We'll also create a variable called z that will control how deep into the screen (on the z axis) the crate is.

GLfloat xrot; // X Rotation

GLfloat yrot; // Y Rotation

GLfloat xspeed; // X Rotation Speed

GLfloat yspeed; // Y Rotation Speed

GLfloat z=-5.0f; // Depth Into The Screen

Now we set up the arrays that will be used to create the lighting. We'll use two different types of light. The first type of light is called ambient light. Ambient light is light that doesn't come from any particular direction. All the objects in your scene will be lit up by the ambient light. The second type of light is called diffuse light. Diffuse light is created by your light source and is reflected off the surface of an object in your scene. Any surface of an object that the light hits directly will be very bright, and areas the light barely gets to will be darker. This creates a nice shading effect on the sides of our crate.

Light is created the same way color is created. If the first number is 1.0f, and the next two are 0.0f, we will end up with a bright red light. If the third number is 1.0f, and the first two are 0.0f, we will have a bright blue light. The last number is an alpha value. We'll leave it at 1.0f for now.

So in the line below, we are storing the values for a white ambient light at half intensity (0.5f). Because all the numbers are 0.5f, we will end up with a light that's halfway between off (black) and full brightness (white). Red, blue and green mixed at the same value will create a shade from black(0.0f) to white(1.0f). Without an ambient light, spots where there is no diffuse light will appear very dark.

GLfloat LightAmbient[]= { 0.5f, 0.5f, 0.5f, 1.0f }; // Ambient Light Values ( NEW )

In the next line we're storing the values for a super bright, full intensity diffuse light. All the values are 1.0f. This means the light is as bright as we can get it. A diffuse light this bright lights up the front of the crate nicely.

GLfloat LightDiffuse[]= { 1.0f, 1.0f, 1.0f, 1.0f }; // Diffuse Light Values ( NEW )

Finally we store the position of the light. The first three numbers are the same as glTranslate's three numbers. The first number is for moving left and right on the x plane, the second number is for moving up and down on the y plane, and the third number is for moving into and out of the screen on the z plane. Because we want our light hitting directly on the front of the crate, we don't move left or right so the first value is 0.0f (no movement on x), we don't want to move up and down, so the second value is 0.0f as well. For the third value we want to make sure the light is always in front of the crate. So we'll position the light off the screen, towards the viewer. Lets say the glass on your monitor is at 0.0f on the z plane. We'll position the light at 2.0f on the z plane. If you could actually see the light, it would be floating in front of the glass on your monitor. By doing this, the only way the light would be behind the crate is if the crate was also in front of the glass on your monitor. Of course if the crate was no longer behind the glass on your monitor, you would no longer see the crate, so it doesn't matter where the light is. Does that make sense?