support fire effect with alpha blending

main algorithm has been revised

1 files changed, 121 insertions, 36 deletions

diff --git a/effect-pad.c b/effect-pad.c
index dae1a02..0911701 100644
--- a/effect-pad.c
+++ b/effect-pad.c
@@ -1,12 +1,15 @@
 #include <stdio.h>
 #include <stdlib.h>
+#include <string.h>
 #include <assert.h>
 
 #include <SDL.h>
 #include <SDL_image.h>
 
+//#define EFFECT_FIRE_COLORKEYED
+
 #define NARRAY(ARRAY) \
-	(sizeof(ARRAY) / sizeof(ARRAY[0]))
+	(sizeof(ARRAY) / sizeof((ARRAY)[0]))
 
 #define SDL_MAYBE_LOCK(SURFACE) do {		\
 	if (SDL_MUSTLOCK(SURFACE))		\
@@ -33,61 +36,140 @@
 
 static SDL_Surface *screen;
 
+static SDL_Color colors[256];
+
+#define FIRE_DECAY(C) \
+	((C) > 0 ? (C) - 1 : 0)
+
 static inline SDL_Surface *
 effect_fire_init(void)
 {
+	Uint32 flags = SDL_HWSURFACE;
 	SDL_Surface *surface;
-	static SDL_Color colors[256];
 
-	surface = SDL_CreateRGBSurface(SDL_HWSURFACE | SDL_SRCCOLORKEY,
-				       screen->w, screen->h, 8, 0, 0, 0, 0);
+#ifdef EFFECT_FIRE_COLORKEYED
+	surface = SDL_CreateRGBSurface(flags, screen->w, screen->h, 8,
+				       0, 0, 0, 0);
+#else
+	flags |= SDL_SRCALPHA;
+	surface = SDL_CreateRGBSurface(flags, screen->w, screen->h, 32,
+				       0x000000FF, 0x0000FF00,
+				       0x00FF0000, 0xFF000000);
+#endif
 	if (surface == NULL) {
 		SDL_ERROR("SDL_CreateRGBSurface");
 		exit(EXIT_FAILURE);
 	}
 
+#ifdef EFFECT_FIRE_COLORKEYED
 	if (SDL_SetColorKey(surface, SDL_SRCCOLORKEY, 0)) {
 		SDL_ERROR("SDL_SetColorKey");
 		SDL_FreeSurface(surface);
 		exit(EXIT_FAILURE);
 	}
+#endif
+
+	memset(colors, 0, sizeof(colors));
 
 	for (int i = 0; i < 32; i++) {
+#ifdef EFFECT_FIRE_COLORKEYED
 		/* black to blue, 32 values */
 		colors[i].b = i << 1;
+#else
+		/* transparent to blue, 32 values */
+		colors[i].b = 255;
+		colors[i].unused = i << 3;
+#endif
 
 		/* blue to red, 32 values */
 		colors[i + 32].r = i << 3;
-		colors[i + 32].b =  64 - (i << 1);
+		colors[i + 32].b = 64 - (i << 1);
+		colors[i + 32].unused = SDL_ALPHA_OPAQUE;
 
 		/*red to yellow, 32 values */
 		colors[i + 64].r = 255;
 		colors[i + 64].g = i << 3;
+		colors[i + 64].unused = SDL_ALPHA_OPAQUE;
 
 		/* yellow to white, 162 */
 		colors[i + 96].r = 255;
 		colors[i + 96].g = 255;
 		colors[i + 96].b = i << 2;
+		colors[i + 96].unused = SDL_ALPHA_OPAQUE;
 		colors[i + 128].r = 255;
 		colors[i + 128].g = 255;
 		colors[i + 128].b = 64 + (i << 2);
+		colors[i + 128].unused = SDL_ALPHA_OPAQUE;
 		colors[i + 160].r = 255;
 		colors[i + 160].g = 255;
 		colors[i + 160].b = 128 + (i << 2);
+		colors[i + 160].unused = SDL_ALPHA_OPAQUE;
 		colors[i + 192].r = 255;
 		colors[i + 192].g = 255;
 		colors[i + 192].b = 192 + i;
+		colors[i + 192].unused = SDL_ALPHA_OPAQUE;
 		colors[i + 224].r = 255;
 		colors[i + 224].g = 255;
 		colors[i + 224].b = 224 + i;
+		colors[i + 224].unused = SDL_ALPHA_OPAQUE;
 	}
 
+#ifdef EFFECT_FIRE_COLORKEYED
 	SDL_SetPalette(surface, SDL_LOGPAL | SDL_PHYSPAL, colors,
-		       0, NARRAY(colors)); 
+		       0, NARRAY(colors));
+#else
+	SDL_FillRect(surface, NULL,
+		     SDL_MapRGBA(surface->format,
+		     	     	 colors[0].r, colors[0].g,
+		     	     	 colors[0].b, colors[0].unused));
+#endif
 
 	return surface;
 }
 
+#ifdef EFFECT_FIRE_COLORKEYED
+
+static inline Uint8
+effect_fire_get_color(SDL_Surface *surface, int x, int y)
+{
+	return ((Uint8 *)surface->pixels)[surface->w*y + x];
+}
+
+static inline void
+effect_fire_set_color(SDL_Surface *surface, int x, int y, Uint8 color)
+{
+	((Uint8 *)surface->pixels)[surface->w*y + x] = color;
+}
+
+#else
+
+static inline Uint8
+effect_fire_get_color(SDL_Surface *surface, int x, int y)
+{
+	SDL_Color color;
+
+	/* alpha-channel surface */
+	SDL_GetRGBA(((Uint32 *)surface->pixels)[surface->w*y + x],
+		    surface->format, &color.r, &color.g, &color.b, &color.unused);
+	for (Uint8 i = 0; i < NARRAY(colors); i++)
+		if (!memcmp(colors + i, &color, sizeof(color)))
+			return i;
+
+	/* shouldn't be reached */
+	return 0;
+}
+
+static inline void
+effect_fire_set_color(SDL_Surface *surface, int x, int y, Uint8 color)
+{
+	((Uint32 *)surface->pixels)[surface->w*y + x] =
+		SDL_MapRGBA(surface->format,
+			    colors[color].r, colors[color].g,
+			    colors[color].b, colors[color].unused);
+}
+
+#endif
+
 static inline void
 effect_fire_update(SDL_Surface *surface)
 {
@@ -95,38 +177,41 @@ effect_fire_update(SDL_Surface *surface)
 
 	SDL_MAYBE_LOCK(surface);
 
-	if (SDL_GetMouseState(&mouse_x, &mouse_y) & SDL_BUTTON(1)) {
-		Uint8 *p = (Uint8 *)surface->pixels;
-		float r = (float)rand()/RAND_MAX;
-
-		p[mouse_y*surface->pitch + mouse_x] = r > .3 ? 255 : 0;
-	}
-
-	for (Uint8 *p = (Uint8 *)surface->pixels + surface->pitch*surface->h - 1;
-	     p >= (Uint8 *)surface->pixels + surface->pitch;
-	     p--) {
-		Uint16 acc;
-
-		if (!((p - (Uint8 *)surface->pixels) % surface->pitch)) {
-			/* left edge */
-			acc = (Uint16)p[0] + p[1];
-			if (acc/2 > p[-surface->pitch])
-				p[-surface->pitch] = (acc + p[-surface->pitch])/3;
-		} else if (!((p - (Uint8 *)surface->pixels + 1) % surface->pitch)) {
-			/* right edge */
-			acc = (Uint16)p[-1] + p[0];
-			if (acc/2 > p[-surface->pitch])
-				p[-surface->pitch] = (acc + p[-surface->pitch])/3;
-		} else {
-			/* somewhere inbetween */
-			acc = (Uint16)p[-1] + p[0] + p[1];
-			if (acc/3 > p[-surface->pitch])
-				p[-surface->pitch] = (acc + p[-surface->pitch])/4;
+	if (SDL_GetMouseState(&mouse_x, &mouse_y) & SDL_BUTTON(1))
+		effect_fire_set_color(surface, mouse_x, mouse_y,
+				      (float)rand()/RAND_MAX > .3 ? 255 : 0);
+
+	for (int y = surface->h - 1; y > 0; y--) {
+		Uint16	acc;
+		Uint8	color;
+
+		/* right edge */
+		acc = (Uint16)effect_fire_get_color(surface, surface->w - 2, y)
+		    + effect_fire_get_color(surface, surface->w - 1, y);
+		color = effect_fire_get_color(surface, surface->w - 1, y - 1);
+		if (acc/2 > color)
+			color = (Uint8)((acc + color)/3);
+		effect_fire_set_color(surface, surface->w - 1, y - 1,
+				      FIRE_DECAY(color));
+
+		/* center */
+		for (int x = surface->w - 2; x > 0; x--) {
+			acc = (Uint16)effect_fire_get_color(surface, x - 1, y)
+			    + effect_fire_get_color(surface, x, y)
+			    + effect_fire_get_color(surface, x + 1, y);
+			color = effect_fire_get_color(surface, x, y - 1);
+			if (acc/3 > color)
+				color = (Uint8)((acc + color)/4);
+			effect_fire_set_color(surface, x, y - 1, FIRE_DECAY(color));
 		}
 
-		/* decay */
-		if (p[-surface->pitch] > 0)
-			p[-surface->pitch]--;
+		/* left edge */
+		acc = (Uint16)effect_fire_get_color(surface, 0, y)
+		    + effect_fire_get_color(surface, 1, y);
+		color = effect_fire_get_color(surface, 0, y - 1);
+		if (acc/2 > color)
+			color = (Uint8)((acc + color)/3);
+		effect_fire_set_color(surface, 0, y - 1, FIRE_DECAY(color));
 	}
 
 	SDL_MAYBE_UNLOCK(surface);