Allegro学习笔记五

http://wiki.allegro.cc/AllegroExamples以上是英文例子站点。

by Shawn Hargreaves,allegro的作者

目录： 1 Allegro 例子

1.1 exhello
1.2 exmem
1.3 expat
1.4 expal
1.5 exflame

这个例子展示了如何“直接在显存中写数据”的技巧
它实现了“火焰”的特效。
第1次使用getpixel() 和 putpixel(),
接着使用直接访问内存的方式
最后使用“块复制操作”

#include <allegro.h>

/* The fire is formed from several 'hotspots' which are moved randomly
* across the bottom of the screen.
*/
#define FIRE_HOTSPOTS 48

int hotspot[FIRE_HOTSPOTS];

unsigned char *temp;

/* This function updates the bottom line of the screen with a pattern
* of varying intensities which are then moved upwards and faded out
* by the code in main().
*/
void draw_bottom_line_of_fire(void)
{
int c, c2;

/* zero the buffer */
for (c=0; c<SCREEN_W; c++)
temp[c] = 0;

for (c=0; c<FIRE_HOTSPOTS; c++) {
/* display the hotspots */
for (c2=hotspot[c]-20; c2<hotspot[c]+20; c2++)
if ((c2 >= 0) && (c2 < SCREEN_W))
temp[c2] = MIN(temp[c2] + 20-ABS(hotspot[c]-c2), 192);

/* move the hotspots */
hotspot[c] += (AL_RAND() & 7) - 3;
if (hotspot[c] < 0)
hotspot[c] += SCREEN_W;
else
if (hotspot[c] >= SCREEN_W)
hotspot[c] -= SCREEN_W;
}

/* display the buffer */
for (c=0; c<SCREEN_W; c++)
putpixel(screen, c, SCREEN_H-1, temp[c]);
}

int main(void)
{
PALETTE palette;
uintptr_t address;
int x, y, c;

if (allegro_init() != 0)
return 1;
install_keyboard();
if (set_gfx_mode(GFX_AUTODETECT, 320, 200, 0, 0) != 0) {
if (set_gfx_mode(GFX_AUTODETECT, 640, 480, 0, 0) != 0) {
allegro_message("Error setting graphics mode\n%s\n", allegro_error);
return 1;
}
}

temp = (unsigned char *)malloc(sizeof(unsigned char) * SCREEN_W);

if (!temp) {
set_gfx_mode(GFX_TEXT, 0, 0, 0, 0);
allegro_message("Not enough memory? This is a joke right!?!\n");
return 0;
}

for (c=0; c<FIRE_HOTSPOTS; c++)
hotspot[c] = AL_RAND() % SCREEN_W;

/* fill our palette with a gradually altering sequence of colors */
for (c=0; c<64; c++) {
palette[c].r = c;
palette[c].g = 0;
palette[c].b = 0;
}
for (c=64; c<128; c++) {
palette[c].r = 63;
palette[c].g = c-64;
palette[c].b = 0;
}
for (c=128; c<192; c++) {
palette[c].r = 63;
palette[c].g = 63;
palette[c].b = c-128;
}
for (c=192; c<256; c++) {
palette[c].r = 63;
palette[c].g = 63;
palette[c].b = 63;
}

set_palette(palette);

textout_ex(screen, font, "Using get/putpixel()", 0, 0, makecol(255,255,255), makecol(0, 0, 0));

/* using getpixel() and putpixel() is slow :-) */
while (!keypressed()) {
acquire_screen();

draw_bottom_line_of_fire();

for (y=64; y<SCREEN_H-1; y++) {
/* read line */
for (x=0; x<SCREEN_W; x++) {
c = getpixel(screen, x, y+1);

if (c > 0)
c--;

putpixel(screen, x, y, c);
}
}
release_screen();
}

clear_keybuf();
textout_ex(screen, font, "Using direct memory writes", 0, 0, makecol(255,255,255), makecol(0, 0, 0));

/* It is much faster if we access the screen memory directly. This
* time we read an entire line of the screen into our own buffer,
* modify it there, and then write the whole line back in one go.
* That is to avoid having to keep switching back and forth between
* different scanlines: if we only copied one pixel at a time, we
* would have to call bmp_write_line() for every single pixel rather
* than just twice per line.
*/
while (!keypressed()) {
acquire_screen();
draw_bottom_line_of_fire();

bmp_select(screen);

for (y=64; y<SCREEN_H-1; y++) {
/* get an address for reading line y+1 */
address = bmp_read_line(screen, y+1);

/* read line with farptr functions */
for (x=0; x<SCREEN_W; x++)
temp[x] = bmp_read8(address+x);

/* adjust it */
for (x=0; x<SCREEN_W; x++)
if (temp[x] > 0)
temp[x]--;

/* get an address for writing line y */
address = bmp_write_line(screen, y);

/* write line with farptr functions */
for (x=0; x<SCREEN_W; x++)
bmp_write8(address+x, temp[x]);
}

bmp_unwrite_line(screen);
release_screen();
}

clear_keybuf();
textout_ex(screen, font, "Using block data transfers", 0, 0, makecol(255,255,255), makecol(0, 0, 0));

/* It is even faster if we transfer the data in 32 bit chunks, rather
* than only one pixel at a time. This method may not work on really
* unusual machine architectures, but should be ok on just about
* anything that you are practically likely to come across.
*/
while (!keypressed()) {
acquire_screen();
draw_bottom_line_of_fire();

bmp_select(screen);

for (y=64; y<SCREEN_H-1; y++) {
/* get an address for reading line y+1 */
address = bmp_read_line(screen, y+1);

/* read line in 32 bit chunks */
for (x=0; x<SCREEN_W; x += sizeof(uint32_t))
*((uint32_t *)&temp[x]) = bmp_read32(address+x);

/* adjust it */
for (x=0; x<SCREEN_W; x++)
if (temp[x] > 0)
temp[x]--;

/* get an address for writing line y */
address = bmp_write_line(screen, y);

/* write line in 32 bit chunks */
for (x=0; x<SCREEN_W; x += sizeof(uint32_t))
bmp_write32(address+x, *((uint32_t *)&temp[x]));
}

bmp_unwrite_line(screen);
release_screen();
}

free(temp);

return 0;
}

END_OF_MAIN()

--------------------------------------------------------------------------------------------------------------------------------------------------

小结五：

PS:这个例子与我手头上的工作关系不是很大，因此暂时放一下。回头再来对付

--------------------------------------------------------------------------------------------------------------------------------------------------

使用allegro的公式：
1、allegro_init(); // 必须的
2、install_keyboard(); // 初始化
install_mouse();

3、set_gfx_mode(标志量,屏幕宽,屏幕高,0,0); // 设置显示模式
4、set_palette(black_palette); // 设置调色板

5、绘制(直接写屏、文字输出、新建位图，位图拷贝);
show_mouse(screen);

6、响应用户输入事件(主循环)

readkey();
keypress();

7、END_OF_MAIN // 必须的