add fade_slide transition to lua slides

resources/slides.lua

 
 function make_paint(size, color)
     local paint = Sk.newPaint();
     paint:setAntiAlias(true)
     paint:setSubpixelText(true)
     paint:setTextSize(size)
     paint:setColor(color)
     return paint
 end
 
@@ skipping 51 matching lines @@
     else
         rec.prevImage = next
         rec.nextImage = prev
         rec.curr_x = -640
         rec.step_x = 15
         rec.isDone = function (self) return self.curr_x >= 0 end
     end
     return rec
 end
 
+function fade_slide_transition(prev, next, is_forward)
+    local rec = {
+        prevImage = prev,
+        nextImage = next,
+        proc = function(self, canvas, drawSlideProc)
+            if self:isDone() then
+                drawSlideProc(canvas)
+                return nil
+            end
+            canvas:drawImage(self.prevImage, self.prev_x, 0, self.prev_a)
+            canvas:drawImage(self.nextImage, self.next_x, 0, self.next_a)
+            self:step()
+            return self
+        end
+    }
+    if is_forward then
+        rec.prev_x = 0
+        rec.prev_a = 1
+        rec.next_x = 640
+        rec.next_a = 0
+        rec.isDone = function (self) return self.next_x <= 0 end
+        rec.step = function (self)
+            self.next_x = self.next_x - 20
+            self.next_a = (640 - self.next_x) / 640
+            self.prev_a = 1 - self.next_a
+        end
+    else
+        rec.prev_x = 0
+        rec.prev_a = 1
+        rec.next_x = 0
+        rec.next_a = 0
+        rec.isDone = function (self) return self.prev_x >= 640 end
+        rec.step = function (self)
+            self.prev_x = self.prev_x + 20
+            self.prev_a = (640 - self.prev_x) / 640
+            self.next_a = 1 - self.prev_a
+        end
+    end
+    return rec
+end
+
 --------------------------------------------------------------------------------------
 
 gTemplate = {
     title = { x = 10, y = 64, textSize = 64 },
     child = { x = 40, y = 120, dy = 50, textSize = 40 },
 }
 
 gPaints = {}
 gPaints.title = make_paint(gTemplate.title.textSize, { a=1, r=0, g=0, b=0 } )
 gPaints.child = make_paint(gTemplate.child.textSize, { a=.75, r=0, g=0, b=0 } )
 
 gRedPaint = Sk.newPaint()
 gRedPaint:setAntiAlias(true)
 gRedPaint:setColor{a=1, r=1, g=0, b=0 }
 
 gSlides = {
     {   text = "Title1", style="title", color = { a=1, r=1, g=0, b=0 },
         children = {
             {   text = "bullet 1", style = "child" },
             {   text = "bullet 2", style = "child" },
             {   text = "bullet 3", style = "child" },
             {   draw = function (canvas)
                     canvas:drawOval({left=300, top=300, right=400, bottom=400}, gRedPaint)
             end },
         },
-        transition = slide_transition
+        transition = fade_slide_transition
     },
     {   text = "Title2", style="title", color = { a=1, r=0, g=1, b=0 },
         children = {
             {   text = "bullet uno", style = "child" },
             {   text = "bullet 2", style = "child" },
             {   text = "bullet tres", style = "child" },
         },
-        transition = fade_transition
+        transition = slide_transition
     },
     {   text = "Title3", style="title",
         children = {
             {   text = "bullet 1", style = "child", },
             {   text = "bullet 2", style = "child", color = { r=0, g=0, b=1 } },
             {   text = "bullet 3", style = "child" },
         }
     }
 }
 
@@ skipping 153 matching lines @@
 }
 
 function onCharHandler(uni)
     local proc = keyProcs[uni]
     if proc then
         proc()
         return true
     end
     return false
 end