First try on zooming

image.c

@@ -88,6 +88,28 @@ void img_display(img_t *img, win_t *win) {
 	img_render(img, win);
 }
 
+void img_check_pan(img_t *img, win_t *win) {
+	if (!img)
+		return;
+
+	if (img->w * img->zoom > win->w) {
+		if (img->x > 0 && img->x + img->w * img->zoom > win->w)
+			img->x = 0;
+		if (img->x < 0 && img->x + img->w * img->zoom < win->w)
+			img->x = win->w - img->w * img->zoom;
+	} else {
+		img->x = (win->w - img->w * img->zoom) / 2;
+	}
+	if (img->h * img->zoom > win->h) {
+		if (img->y > 0 && img->y + img->h * img->zoom > win->h)
+			img->y = 0;
+		if (img->y < 0 && img->y + img->h * img->zoom < win->h)
+			img->y = win->h - img->h * img->zoom;
+	} else {
+		img->y = (win->h - img->h * img->zoom) / 2;
+	}
+}
+
 void img_render(img_t *img, win_t *win) {
 	int sx, sy, sw, sh;
 	int dx, dy, dw, dh;
@@ -95,6 +117,8 @@ void img_render(img_t *img, win_t *win) {
 	if (!img || !win || !imlib_context_get_image())
 		return;
 
+	img_check_pan(img, win);
+
 	if (img->x < 0) {
 		sx = -img->x / img->zoom;
 		sw = win->w / img->zoom;
@@ -125,3 +149,41 @@ void img_render(img_t *img, win_t *win) {
 
 	win_draw(win);
 }
+
+int img_zoom(img_t *img, int d) {
+	int ad, iz;
+	float z;
+
+	if (!img)
+		return 0;
+
+	ad = ABS(d);
+	iz = (int) (img->zoom * 1000.0) + d;
+	if (iz % ad > ad / 2)
+		iz += ad - iz % ad;
+	else
+		iz -= iz % ad;
+	z = (float) iz / 1000.0;
+
+	if (z * 100.0 < ZOOM_MIN)
+		z = ZOOM_MIN / 100.0;
+	else if (z * 100.0 > ZOOM_MAX)
+		z = ZOOM_MAX / 100.0;
+
+	if (z != img->zoom) {
+		img->x -= (img->w * z - img->w * img->zoom) / 2;
+		img->y -= (img->h * z - img->h * img->zoom) / 2;
+		img->zoom = z;
+		return 1;
+	} else {
+		return 0;
+	}
+}
+
+int img_zoom_in(img_t *img) {
+	return img_zoom(img, 125);
+}
+
+int img_zoom_out(img_t *img) {
+	return img_zoom(img, -125);
+}

image.h

@@ -43,4 +43,7 @@ int img_load(img_t*, const char*);
 void img_display(img_t*, win_t*);
 void img_render(img_t*, win_t*);
 
+int img_zoom_in(img_t*);
+int img_zoom_out(img_t*);
+
 #endif /* IMAGE_H */

main.c

@@ -142,6 +142,19 @@ void on_keypress(XEvent *ev) {
 				update_title();
 			}
 			break;
+		case XK_plus:
+		case XK_equal:
+			if (img_zoom_in(&img)) {
+				img_render(&img, &win);
+				update_title();
+			}
+			break;
+		case XK_minus:
+			if (img_zoom_out(&img)) {
+				img_render(&img, &win);
+				update_title();
+			}
+			break;
 	}
 }
 

sxiv.h

@@ -23,6 +23,7 @@
 
 #define VERSION "git-20110119"
 
+#define ABS(a)   ((a) < 0 ? (-(a)) : (a))
 #define MIN(a,b) ((a) < (b) ? (a) : (b))
 #define MAX(a,b) ((a) > (b) ? (a) : (b))