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Chapter 13 Special Effects 250 Fastgraph User's Guide Overview This chapter will discuss the Fastgraph routines that help produce special visual effects. These include the ability to dissolve the screen contents in small increments, scroll areas of the screen, and change the physical origin of the screen. The accompanying example programs illustrate how to use these routines to produce some interesting effects. Screen Dissolving Screen dissolving is the process of replacing the entire screen contents in random small increments instead of all at once. Fastgraph includes two routines, fg_fadeout and fg_fadein, for this purpose. The fg_fadeout routine incrementally replaces the visual page contents with pixels of the current color, while fg_fadein incrementally replaces the visual page contents with the hidden page contents (that is, the page defined in the most recent call to fg_sethpage). Both routines accept an integer argument that defines the delay between each incremental replacement. A value of zero means to perform the replacement as quickly as possible, while 1 is slightly slower, 2 is slower yet, and so forth. The fg_fadeout and fg_fadein routines have no effect in text video modes. Example 13-1 shows how to use the fg_fadeout routine. The program, which runs in any graphics video mode, first fills the screen with a rectangle of color 2. After waiting for a keystroke, the program incrementally replaces the screen contents with pixels of color 15 (the current color index when fg_fadeout is called). After another keystroke, the program exits gracefully. Example 13-1. #include <fastgraf.h> void main(void); void main() { int old_mode; old_mode = fg_getmode(); fg_setmode(fg_automode()); fg_setcolor(2); fg_rect(0,fg_getmaxx(),0,fg_getmaxy()); fg_waitkey(); fg_setcolor(15); fg_fadeout(0); fg_waitkey(); fg_setmode(old_mode); fg_reset(); } Chapter 13: Special Effects 251 Example 13-2 shows how to use the fg_fadein routine in any 320 by 200 color graphics video mode. The program first fills the screen with a rectangle of color 2 and then fills video page 1 with a rectangle of color 1. After waiting for a keystroke, the program incrementally transfers the contents of page 1 to the visual page. After the call to fg_fadein, both page 0 (the visual page) and page 1 (the hidden page) will contain rectangles of color 1 that fill the entire video page. Finally, the program waits for another keystroke before returning to DOS. Example 13-2. #include <fastgraf.h> #include <stdio.h> #include <stdlib.h> void main(void); void main() { int new_mode, old_mode; new_mode = fg_bestmode(320,200,2); if (new_mode < 0 || new_mode == 12) { printf("This program requires a 320 "); printf("x 200 color graphics mode.\n"); exit(1); } old_mode = fg_getmode(); fg_setmode(new_mode); fg_allocate(1); fg_sethpage(1); fg_setcolor(2); fg_rect(0,319,0,199); fg_setpage(1); fg_setcolor(1); fg_rect(0,319,0,199); fg_waitkey(); fg_fadein(0); fg_waitkey(); fg_freepage(1); fg_setmode(old_mode); fg_reset(); } You also can produce some appealing visual effects by replacing the screen contents in a non-random fashion using the fg_restore or fg_transfer routines. For example, you could copy the hidden page contents to the visual page through a series of concentric rectangular areas, each slightly larger than the previous, until the entire screen is copied. Another interesting effect is to start around the screen perimeter and proceed toward the screen center, thus producing a "snake-like" effect. Experimenting with such techniques may reveal other effects that suit your application. 252 Fastgraph User's Guide Scrolling Another useful effect is scrolling, and Fastgraph provides a routine that performs vertical scrolling within a given region of the active video page. The fg_scroll routine scrolls a region defined in screen space or character space. It can scroll up or down and offers two types of scrolling: circular and end-off. In circular scrolling, rows that scroll off one edge of the defined region appear at its opposite edge. In end-off scrolling, such rows are simply wind up above or below the scrolling area. The following diagrams illustrate the two types of scrolling. end-off scrolling circular scrolling before after before after C B A A A A B B In these diagrams, the area bounded by the double lines is the scrolling region, as specified in the call to fg_scroll. Also, the scrolling direction is assumed to be down (that is, toward the bottom of the screen), and the number of rows to scroll is the height of the area designated B. The number of rows to scroll is often called the scrolling increment. For the end-off scrolling example, the scrolling operation transfers region A downward so part of it is copied into area B. The area C (which is the same size as area B) at the top of the scrolling region is filled with pixels of the current color index (as defined in the most recent call to fg_setcolor), and the original contents of area B are lost. The circular scrolling example also copies region A downward into the original area B. Unlike end-off scrolling, however, circular scrolling preserves the area B by copying it to the opposite edge of the scrolling region. The fg_scroll routine takes six arguments. The first four define the scrolling region in the order minimum x coordinate, maximum x coordinate, minimum y coordinate, and maximum y coordinate. In graphics video modes, the x coordinates are extended by byte boundaries if needed. The fifth argument is the scrolling increment. It specifies the number of rows to scroll. If it is positive, the scrolling direction is toward the bottom of the screen; if it is negative, the scrolling direction is toward the top of the screen. The sixth and final argument specifies the scroll type. If this value is zero, the scroll will be circular; if it is any other value, the scroll will be end-off. If the scroll type is circular, Fastgraph will use the hidden page (as defined in the most recent call to fg_sethpage) as a workspace (more specifically, the area bounded by the scrolling region extremes on the hidden page will be used). We'll now present three example programs that use the fg_scroll routine. Example 13-3 runs in any 320 by 200 graphics video mode. The program displays two lines of text ("line one" and "line two") in the upper left corner of the screen against a white background. It then uses the fg_scroll routine to move the second line down four pixel rows using an end-off scroll. Chapter 13: Special Effects 253 After waiting for a keystroke, the program again uses fg_scroll to move the text back to its original position. Note especially how the fg_setcolor routine appears before the first call to fg_scroll to replace the "scrolled off" rows with pixels of color 15, thus preserving the white background. Example 13-3. #include <fastgraf.h> #include <stdio.h> #include <stdlib.h> void main(void); void main() { int new_mode, old_mode; new_mode = fg_bestmode(320,200,1); if (new_mode < 0 || new_mode == 12) { printf("This program requires a 320 "); printf("x 200 color graphics mode.\n"); exit(1); } old_mode = fg_getmode(); fg_setmode(new_mode); fg_setcolor(15); fg_rect(0,319,0,199); fg_setcolor(10); fg_text("line one",8); fg_locate(1,0); fg_text("line two",8); fg_waitkey(); fg_setcolor(15); fg_scroll(0,63,8,15,4,1); fg_waitkey(); fg_scroll(0,63,12,19,-4,1); fg_waitkey(); fg_setmode(old_mode); fg_reset(); } Example 13-4 is similar to example 13-3, but it runs in the 80-column color text mode (mode 3). In text modes, we cannot scroll half a character row (four pixels) as in example 13-3, so the program scrolls the minimum one row instead. Example 13-4. #include <fastgraf.h> void main(void); void main() { int old_mode; 254 Fastgraph User's Guide old_mode = fg_getmode(); fg_setmode(3); fg_cursor(0); fg_setcolor(7); fg_rect(0,79,0,24); fg_setattr(10,7,0); fg_text("line one",8); fg_locate(1,0); fg_text("line two",8); fg_waitkey(); fg_setcolor(7); fg_scroll(0,7,1,1,1,1); fg_waitkey(); fg_scroll(0,7,2,2,-1,1); fg_waitkey(); fg_setmode(old_mode); fg_reset(); } Example 13-5, the final scrolling example, demonstrates a circular scroll. The program runs in any 320 by 200 color graphics video mode; note the use of video page 1 for the workspace required when the fg_scroll routine performs a circular scroll. The program first fills the screen with a light blue rectangle (cyan in CGA), displays a smaller white rectangle in the center of the screen, and then uses fg_move, fg_draw, and fg_paint to display a light green star (magenta in CGA) within the white rectangle. The program executes a while loop to scroll the star upward in four pixel increments. Because the scroll is circular, rows of the star that "scroll off" the top edge of the white rectangle (whose height is the same as the scrolling region) reappear at its bottom edge. The use of fg_waitfor within the loop simply slows down the scroll. The scrolling continues until any key is pressed. Example 13-5. #include <conio.h> #include <fastgraf.h> #include <stdio.h> #include <stdlib.h> void main(void); void main() { int new_mode, old_mode; new_mode = fg_bestmode(320,200,2); if (new_mode < 0 || new_mode == 12) { printf("This program requires a 320 "); printf("x 200 color graphics mode.\n"); exit(1); } old_mode = fg_getmode(); Chapter 13: Special Effects 255 fg_setmode(new_mode); fg_allocate(1); fg_sethpage(1); fg_setcolor(9); fg_rect(0,319,0,199); fg_setcolor(15); fg_rect(132,188,50,150); fg_setcolor(10); fg_move(160,67); fg_draw(175,107); fg_draw(140,82); fg_draw(180,82); fg_draw(145,107); fg_draw(160,67); fg_paint(160,77); fg_paint(150,87); fg_paint(160,87); fg_paint(170,87); fg_paint(155,97); fg_paint(165,97); while (kbhit() == 0) { fg_waitfor(1); fg_scroll(136,184,50,150,-4,0); } fg_waitkey(); fg_freepage(1); fg_setmode(old_mode); fg_reset(); } Changing the Screen Origin Fastgraph includes two routines for changing the screen origin. By changing the screen origin, we simply mean defining the (x,y) coordinate of the upper left corner of the display area. The fg_pan routine performs this function in screen space, while the fg_panw routine does in world space. Neither routine changes the graphics cursor position. Each of these routines has two arguments that specify the x and y coordinates of the screen origin. For the fg_pan routine, the arguments are integer quantities. For the fg_panw routine, they are floating point quantities. In the EGA, VGA, MCGA, XVGA, and SVGA graphics modes (modes 13 to 29), you can set the screen origin to any (x,y) coordinate position (that is, to any pixel). In the other graphics modes, certain restrictions exist, as imposed by specific video hardware. These constraints limit the coordinate positions that can be used as the screen origin. Fastgraph compensates for these restrictions by reducing the specified x and y coordinates to values that are acceptable to the current video mode, as shown in the following table. 256 Fastgraph User's Guide x will be reduced y will be reduced video mode to a multiple of: to a multiple of: 4-5 8 2 6 16 2 9 4 4 11 8 4 12 4 2 or 3 In modes 4 and 5, for instance, the x coordinate will be reduced to a multiple of 8 pixels, and the y coordinate will be reduced to a multiple of 2 pixels. In the Hercules low resolution mode (mode 12), the y coordinate reduction depends on whether or not the specified pixel row is scan doubled. Example 13-6 shows a useful effect that can be made with the fg_pan or fg_panw routines. This program uses the fg_automode routine to select a video mode and then draws an unfilled white rectangle. The top and bottom sides of the rectangle are intentionally drawn just smaller than the physical screen size. After waiting for a keystroke, the program uses a for loop to make the rectangle jiggle up and down. The rectangle moves because the fg_pan routine is called inside the loop to switch the screen origin between the rectangle's upper left corner and the original origin. Note also the use of the fg_waitfor routine to cause slight delays after each call to fg_pan. If we didn't use fg_waitfor, the changing of the origin would occur so rapidly we wouldn't notice the effect. Finally, the program restores the original video mode and screen attributes before returning to DOS. Example 13-6. #include <fastgraf.h> #include <stdio.h> #include <stdlib.h> void main(void); #define DELAY 2 #define JUMP 4 void main() { int i; int old_mode; old_mode = fg_getmode(); fg_setmode(fg_automode()); fg_setcolor(15); fg_move(0,JUMP); fg_draw(fg_getmaxx(),JUMP); fg_draw(fg_getmaxx(),fg_getmaxy()-JUMP); fg_draw(0,fg_getmaxy()-JUMP); fg_draw(0,JUMP); fg_waitkey(); for (i = 0; i < 6; i++) { fg_pan(0,JUMP); fg_waitfor(DELAY); Chapter 13: Special Effects 257 fg_pan(0,0); fg_waitfor(DELAY); } fg_setmode(old_mode); fg_reset(); } The real power of the fg_pan routine becomes clear when it is used with the fg_resize routine to perform smooth panning. Recall from Chapter 8 that fg_resize changes the video page dimensions in native EGA and VGA graphics modes (modes 13 to 18), the extended VGA graphics modes (20 to 23), and the SVGA graphics modes (24 to 29). We'll now present an example that shows how to use these two routines to perform panning in the low-resolution EGA graphics mode (mode 13). The method it uses also would work in any mode that supports video page resizing. Example 13-7 begins by establishing the video mode and then immediately calls fg_resize to increase the video page size to 640 by 400 pixels. Thus, the video page is now four times its original size. Following this, the program fills the page (the entire page, not just what is displayed) with a bright green rectangle with a white border around it. It then displays the message "Press arrow keys to pan" as close as possible to the center of the page. The main part of the program is a loop that accepts keystrokes and then calls fg_pan to perform the panning one pixel at a time. When you press any of the four arrow keys, the program adjusts the x and y coordinates for the screen origin as directed. For example, pressing the up arrow key scrolls the screen upward one pixel. Note that when we reach the edge of the video page, the program prevents further scrolling in that direction. This process continues until you press the Esc key, at which time the program restores the original video mode and screen attributes before exiting. Example 13-7. #include <fastgraf.h> void main(void); void main() { unsigned char key, aux; int old_mode; int x, y; old_mode = fg_getmode(); fg_setmode(13); fg_resize(640,400); fg_setcolor(2); fg_rect(0,fg_getmaxx(),0,fg_getmaxy()); fg_setcolor(15); fg_box(0,fg_getmaxx(),0,fg_getmaxy()); fg_locate(24,28); fg_text("Press arrow keys to pan.",24); 258 Fastgraph User's Guide x = 0; y = 0; do { fg_getkey(&key,&aux); if (aux == 72 && y < 200) y++; else if (aux == 75 && x < 320) x++; else if (aux == 77 && x > 0) x--; else if (aux == 80 && y > 0) y--; fg_pan(x,y); } while (key != 27); fg_setmode(old_mode); fg_reset(); } Summary of Special Effects Routines This section summarizes the functional descriptions of the Fastgraph routines presented in this chapter. More detailed information about these routines, including their arguments and return values, may be found in the Fastgraph Reference Manual. FG_FADEIN incrementally replaces the visual page contents with the hidden page contents. This routine has no effect in text video modes. FG_FADEOUT incrementally replaces the visual page contents with pixels of the current color. This routine has no effect in text video modes. FG_PAN changes the screen origin (the upper left corner of the screen) to the specified screen space coordinates. This routine has no effect in text video modes. FG_PANW is the world space version of the fg_pan routine. FG_RESIZE changes the dimensions of a video page in EGA and VGA graphics modes. FG_SCROLL vertically scrolls a region of the active video page. The scrolling may be done either up or down, using either an end-off or circular method. Circular scrolling uses part of the hidden page as a temporary workspace.