Add support for custom move step

Step is specified as a percentage delta of scaled image size.
Stored as a custom parameter in the key binding section of config file:
```
[keys]
Up = zoom_in 10
```

Resolves to #81.

Signed-off-by: Artem Senichev <artemsen@gmail.com>

extra/swayimgrc

@@ -83,14 +83,14 @@ s = animation
 F9 = slideshow
 F11 = fullscreen
 f = fullscreen
-Left = step_left
-h = step_left
-Right = step_right
-l = step_right
-Up = step_up
-k = step_up
-Down = step_down
-j = step_down
+Left = step_left 10
+h = step_left 10
+Right = step_right 10
+l = step_right 10
+Up = step_up 10
+k = step_up 10
+Down = step_down 10
+j = step_down 10
 equal = zoom_in 10
 plus = zoom_in 10
 minus = zoom_out 10

extra/swayimgrc.5

@@ -83,10 +83,10 @@ Valid action are:
 .IP "\fBanimation\fR: start/stop animation;"
 .IP "\fBslideshow\fR: start/stop slideshow;"
 .IP "\fBfullscreen\fR: switch fullscreen mode;"
-.IP "\fBstep_left\fR: move viewport left;"
-.IP "\fBstep_right\fR: move viewport right;"
-.IP "\fBstep_up\fR: move viewport up;"
-.IP "\fBstep_down\fR: move viewport down;"
+.IP "\fBstep_left \fI[PERCENT]\fR\fR: move viewport left, default is 10%;"
+.IP "\fBstep_right \fI[PERCENT]\fR\fR: move viewport right, default is 10%;"
+.IP "\fBstep_up \fI[PERCENT]\fR\fR: move viewport up, default is 10%;"
+.IP "\fBstep_down \fI[PERCENT]\fR\fR: move viewport down, default is 10%;"
 .IP "\fBzoom_in\fR \fI[PERCENT]\fR: zoom in, by default increases scale by 10%;"
 .IP "\fBzoom_out\fR \fI[PERCENT]\fR: zoom out, by default decreases scale by 10%;"
 .IP "\fBzoom_optimal\fR: set to optimal zoom (100% or less to fit to window);"
@@ -115,10 +115,11 @@ info = yes
 font = monospace 14
 font-color = #b4b3b2
 sway = no
+
 [keys]
 q = quit
-r = exec rm "%"
-R = exec echo "%" > mylist.txt
+Up = step_up 5
+e = exec echo "%" > mylist.txt
 .EE
 .\" related man pages
 .SH SEE ALSO

src/canvas.c

@@ -356,43 +356,20 @@ void canvas_print_info(argb_t* wnd, size_t num, const struct info_table* info)
     }
 }
 
-bool canvas_move(enum canvas_move mv)
+bool canvas_move(bool horizontal, ssize_t percent)
 {
-    const size_t scaled_width = ctx.scale * ctx.image.width;
-    const size_t scaled_height = ctx.scale * ctx.image.height;
-    const size_t step_x = ctx.window.width / 10;
-    const size_t step_y = ctx.window.height / 10;
-    ssize_t prev_x = ctx.image.x;
-    ssize_t prev_y = ctx.image.y;
-
-    switch (mv) {
-        case cm_center:
-            ctx.image.x = ctx.window.width / 2 - scaled_width / 2;
-            ctx.image.y = ctx.window.height / 2 - scaled_height / 2;
-            break;
-        case cm_cnt_hor:
-            ctx.image.x = ctx.window.width / 2 - scaled_width / 2;
-            break;
-        case cm_cnt_vert:
-            ctx.image.y = ctx.window.height / 2 - scaled_height / 2;
-            break;
-        case cm_step_left:
-            ctx.image.x += step_x;
-            break;
-        case cm_step_right:
-            ctx.image.x -= step_x;
-            break;
-        case cm_step_up:
-            ctx.image.y += step_y;
-            break;
-        case cm_step_down:
-            ctx.image.y -= step_y;
-            break;
+    const ssize_t old_x = ctx.image.x;
+    const ssize_t old_y = ctx.image.y;
+
+    if (horizontal) {
+        ctx.image.x += (ctx.window.width / 100) * percent;
+    } else {
+        ctx.image.y += (ctx.window.height / 100) * percent;
     }
 
     fix_viewport();
 
-    return (ctx.image.x != prev_x || ctx.image.y != prev_y);
+    return (ctx.image.x != old_x || ctx.image.y != old_y);
 }
 
 void canvas_zoom(ssize_t percent)
@@ -452,7 +429,11 @@ void canvas_set_scale(enum canvas_scale sc)
             break;
     }
 
-    canvas_move(cm_center);
+    // center viewport
+    ctx.image.x = ctx.window.width / 2 - (ctx.scale * ctx.image.width) / 2;
+    ctx.image.y = ctx.window.height / 2 - (ctx.scale * ctx.image.height) / 2;
+
+    fix_viewport();
 }
 
 float canvas_get_scale(void)

src/canvas.h

@@ -6,17 +6,6 @@
 
 #include "types.h"
 
-/** Viewport movement. */
-enum canvas_move {
-    cm_center,     ///< Center of the image
-    cm_cnt_hor,    ///< Center horizontally
-    cm_cnt_vert,   ///< Center vertically
-    cm_step_left,  ///< One step to the left
-    cm_step_right, ///< One step to the right
-    cm_step_up,    ///< One step up
-    cm_step_down   ///< One step down
-};
-
 /** Scaling operations. */
 enum canvas_scale {
     cs_fit_or100,   ///< Fit to window, but not more than 100%
@@ -87,10 +76,11 @@ void canvas_print_info(argb_t* wnd, size_t num, const struct info_table* info);
 
 /**
  * Move viewport.
- * @param mv viewport movement direction
+ * @param horizontal axis along which to move (false for vertical)
+ * @param percent percentage increment to current position
  * @return true if coordinates were changed
  */
-bool canvas_move(enum canvas_move mv);
+bool canvas_move(bool horizontal, ssize_t percent);
 
 /**
  * Zoom in/out.

src/viewer.c

@@ -303,6 +303,33 @@ static void zoom_image(bool zoom_in, const char* params)
     canvas_zoom(percent);
 }
 
+/**
+ * Move viewport.
+ * @param horizontal axis along which to move (false for vertical)
+ * @param positive direction (increase/decrease)
+ * @param params optional move step in percents
+ */
+static bool move_viewport(bool horizontal, bool positive, const char* params)
+{
+    ssize_t percent = 10;
+
+    if (params) {
+        char* endptr;
+        const unsigned long val = strtoul(params, &endptr, 0);
+        if (val != 0 && val <= 1000 && !*endptr) {
+            percent = val;
+        } else {
+            fprintf(stderr, "Invalid move step: \"%s\"\n", params);
+        }
+    }
+
+    if (!positive) {
+        percent = -percent;
+    }
+
+    return canvas_move(horizontal, percent);
+}
+
 /**
  * Animation timer event handler.
  */
@@ -437,13 +464,13 @@ bool viewer_on_keyboard(xkb_keysym_t key)
             ui_set_fullscreen(config.fullscreen);
             return false;
         case kb_step_left:
-            return canvas_move(cm_step_left);
+            return move_viewport(true, true, kbind->params);
         case kb_step_right:
-            return canvas_move(cm_step_right);
+            return move_viewport(true, false, kbind->params);
         case kb_step_up:
-            return canvas_move(cm_step_up);
+            return move_viewport(false, true, kbind->params);
         case kb_step_down:
-            return canvas_move(cm_step_down);
+            return move_viewport(false, false, kbind->params);
         case kb_zoom_in:
         case kb_zoom_out:
             zoom_image(kbind->action == kb_zoom_in, kbind->params);