Chủ nhiệm Bộ môn Ngô Hữu Phúc ĐỀ CƯƠng chi tiết bài giảNG

4.2. A Basic Game Loop

- Yêu cầu SV chuẩn bị:

Chú ý nghe giảng.

Tích cực tham gia phát biểu ý kiến

Tiết thứ: 11-12 Tuần thứ: 4

- Mục đích, yêu cầu:

• Nắm được cách vẽ điểm, đường thẳng, đường tròn, elipse, đường cong, tam giác, đa giác và cách làm việc với Text, cách tô màu.

- Hình thức tổ chức dạy học: Lý thuyết, bài tập, thực hành, tự học, tự nghiên cứu

- Thời gian: Lý thuyết: 2t; Tự học, tự nghiên cứu: 4t

- Địa điểm: Giảng đường do P2 phân công.

- Nội dung chính:

5.1. The InitGraphics Program

How to initialize a full-screen video mode or window of a particular resolution. Figure 3.1 shows the program running.

Figure 3.1

The InitGraphics program.

Drawing Graphics Primitives

You are able to see every pixel or line in a

vector-based program.

Vector displays are contrasted with bitmapped displays, in which the screen is a bitmap array (the videobuffer).

5.2. Basic 2D graphics

The simplest graphics primitive is obviously the pixel-drawing function, and

Allegro provides one:

void putpixel(BITMAP *bmp, int x, int y, int color)

Figure 3.2 shows the output of the Pixels program, which draws random pixels

on the screen using whatever video mode and resolution you prefer.

Figure 3.8

The Pixels program fills the screen with dots. (The Linux version is shown.)

if (ret != 0) {

allegro message(allegro error);

return 1;

}

//display screen resolution

textprintf ex(screen, font, 0, 0, 15, -1,

"Pixels Program - %dx%d - Press ESC to quit",

SCREEN W, SCREEN H);

//wait for keypress

while(!key[KEY ESC])

{

//set a random location

x = 10 + rand() % (SCREEN W-20);

y = 10 + rand() % (SCREEN H-20);

//set a random color

red = rand() % 255;

green = rand() % 255;

blue = rand() % 255;

color = makecol(red,green,blue);

//draw the pixel

putpixel(screen, x, y, color);

}

//end program

allegro exit();

return 0;

}

END OF MAIN()

This program should be clear to you, although it uses a C function called srand to initialize the random-number seed. This program performs a while loop continually until the ESC key is pressed, during which time a pixel of random color and location is drawn using the putpixel function.

The InitGraphics Source Code

The InitGraphics program source code listing follows. Several new functions in

this program are included for convenience; I will go over them shortly. As is the

case with most of the programs in this book, hit the Escape key to quit.