Handle expose events

image.c

@@ -57,10 +57,8 @@ void img_load(img_t *img, const char *filename) {
 	img->h = imlib_image_get_height();
 }
 
-void img_render(img_t *img, win_t *win) {
+void img_display(img_t *img, win_t *win) {
 	float zw, zh;
-	unsigned int sx, sy, sw, sh;
-	unsigned int dx, dy, dw, dh;
 
 	if (!img || !win || !imlib_context_get_image())
 		return;
@@ -84,30 +82,43 @@ void img_render(img_t *img, win_t *win) {
 	img->x = (win->w - img->w * img->zoom) / 2;
 	img->y = (win->h - img->h * img->zoom) / 2;
 
-	if (img->x < 0) {
-		sx = -img->x / img->zoom;
-		sw = (img->x + win->w) / img->zoom;
-		dx = 0;
-		dw = win->w;
+	win_clear(win);
+
+	img_render(img, win, 0, 0, win->w, win->h);
+}
+
+void img_render(img_t *img, win_t *win, int x, int y, int w, int h) {
+	int sx, sy, sw, sh;
+	int dx, dy, dw, dh;
+
+	if (!img || !win || !imlib_context_get_image())
+		return;
+
+	if (img->x < x) {
+		sx = (x - img->x) / img->zoom;
+		sw = MIN(w / img->zoom, img->w - sx);
+		dx = x;
+		dw = sw * img->zoom;
 	} else {
 		sx = 0;
-		sw = img->w;
+		sw = MIN((w - img->x + x) / img->zoom, img->w);
 		dx = img->x;
-		dw = img->w * img->zoom;
+		dw = sw * img->zoom;
 	}
-	if (img->y < 0) {
-		sy = -img->y / img->zoom;
-		sh = (img->y + win->h) / img->zoom;
-		dy = 0;
-		dh = win->h;
+	if (img->y < y) {
+		sy = (y - img->y) / img->zoom;
+		sh = MIN(h / img->zoom, img->h - sy);
+		dy = y;
+		dh = sh * img->zoom;
 	} else {
 		sy = 0;
-		sh = img->h;
+		sh = MIN((h - img->y + y) / img->zoom, img->h);
 		dy = img->y;
-		dh = img->h * img->zoom;
+		dh = sh * img->zoom;
 	}
 
-	win_clear(win);
+	if (sw < 0 || sh < 0)
+		return;
 
 	imlib_render_image_part_on_drawable_at_size(sx, sy, sw, sh, dx, dy, dw, dh);
 }

image.h

@@ -30,16 +30,17 @@ typedef enum scalemode_e {
 typedef struct img_s {
 	float zoom;
 	scalemode_t scalemode;
-	int w;
-	int h;
 	int x;
 	int y;
+	int w;
+	int h;
 } img_t;
 
 void imlib_init(win_t*);
 void imlib_destroy();
 
 void img_load(img_t*, const char*);
-void img_render(img_t*, win_t*);
+void img_display(img_t*, win_t*);
+void img_render(img_t*, win_t*, int, int, int, int);
 
 #endif /* IMAGE_H */

main.c

@@ -69,7 +69,7 @@ int main(int argc, char **argv) {
 	imlib_init(&win);
 
 	img_load(&img, options->filenames[fileidx]);
-	img_render(&img, &win);
+	img_display(&img, &win);
 
 	run();
 
@@ -113,4 +113,9 @@ void on_configurenotify(XEvent *ev) {
 }
 
 void on_expose(XEvent *ev) {
+	if (!ev)
+		return;
+
+	img_render(&img, &win, ev->xexpose.x, ev->xexpose.y,
+	           ev->xexpose.width, ev->xexpose.height);
 }