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

Learning how to texture map has many benefits. Lets say you wanted a missile to fly across the screen. Up until this tutorial we'd probably make the entire missile out of polygons, and fancy colors. With texture mapping, you can take a real picture of a missile and make the picture fly across the screen. Which do you think will look better? A photograph or an object made up of triangles and squares? By using texture mapping, not only will it look better, but your program will run faster. The texture mapped missile would only be one quad moving across the screen. A missile made out of polygons could be made up of hundreds or thousands of polygons. The single texture mapped quad will use alot less processing power.

Lets start off by adding five new lines of code to the top of lesson one. The first new line is #include <stdio.h>. Adding this header file allows us to work with files. In order to use fopen() later in the code we need to include this line. Then we add three new floating point variables… xrot, yrot and zrot. These variables will be used to rotate the cube on the x axis, the y axis, and the z axis. The last line GLuint texture[1] sets aside storage space for one texture. If you wanted to load in more than one texture, you would change the number one to the number of textures you wish to load.

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

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

#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

GLfloat xrot; // X Rotation ( NEW )

GLfloat yrot; // Y Rotation ( NEW )

GLfloat zrot; // Z Rotation ( NEW )

GLuint texture[1]; // Storage For One Texture ( NEW )

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM); // Declaration For WndProc

Now immediately after the above code, and before ReSizeGLScene(), we want to add the following section of code. The job of this code is to load in a bitmap file. If the file doesn't exist NULL is sent back meaning the texture couldn't be loaded. Before I start explaining the code there are a few VERY important things you need to know about the images you plan to use as textures. The image height and width MUST be a power of 2. The width and height must be at least 64 pixels, and for compatability reasons, shouldn't be more than 256 pixels. If the image you want to use is not 64, 128 or 256 pixels on the width or height, resize it in an art program. There are ways around this limitation, but for now we'll just stick to standard texture sizes.

First thing we do is create a file handle. A handle is a value used to identify a resource so that our program can access it. We set the handle to NULL to start off.

AUX_RGBImageRec *LoadBMP(char *Filename) // Loads A Bitmap Image

{

FILE *File=NULL; // File Handle

Next we check to make sure that a filename was actually given. The person may have use LoadBMP() without specifying the file to load, so we have to check for this. We don't want to try loading nothing :)

if (!Filename) // Make Sure A Filename Was Given

{

return NULL; // If Not Return NULL

}

If a filename was given, we check to see if the file exists. The line below tries to open the file.

File=fopen(Filename,"r"); // Check To See If The File Exists

If we were able to open the file it obviously exists. We close the file with fclose(File) then we return the image data. auxDIBImageLoad(Filename) reads in the data.