From 7470cee5f38dd85bceee429ac58ab921289f0c93 Mon Sep 17 00:00:00 2001
From: Junxiao Shi <git@mail1.yoursunny.com>
Date: Tue, 25 Dec 2018 11:51:08 -0500
Subject: [PATCH] processing: preserve scroll position while zooming

This commit makes the Processing program preserve the scroll
position relative to timestamp, when the user is zooming in/out
the graph. Effectively, the left edge of the visible window
always represents the same timestamp, so that the user doesn't
have to search for the interesting region again after zooming.
---
 processing.pde | 66 ++++++++++++++++++++++++++------------------------
 1 file changed, 34 insertions(+), 32 deletions(-)

diff --git a/processing.pde b/processing.pde
index 81105df..7f28c17 100644
--- a/processing.pde
+++ b/processing.pde
@@ -106,7 +106,7 @@ void setup () {
 
 void cleanGraph() {
   noStroke();                                        //no borders
-  fill(black);                                        
+  fill(black);
   rect(xEdge, 0, width, graphBoxH);                  //cancel the graph
   stroke(green);                                     //green lines
   Arrays.fill(xPos, 0);                              //reset start point of the graph
@@ -189,7 +189,7 @@ void drawText() {
 
 
   // write name of the pins
-  fill(white);   
+  fill(white);
   textSize(14);
 
   int x=10;
@@ -236,7 +236,7 @@ void drawText() {
   if (isDraggable) {
     handleX = mouseX-(handleW/2);
     if (handleX<xEdge) handleX = xEdge;
-    if (handleX>width-handleW) handleX = width-handleW;    
+    if (handleX>width-handleW) handleX = width-handleW;
 
     getData();
     xShift = -map(handleX, xEdge, width-handleW, 0, xEnd-900);
@@ -286,7 +286,7 @@ void mouseClicked() {
 
     if (milliseconds == true) {
       for (int i=0; i< samples; i++)  usTime[i] /= 1000.0;
-    } 
+    }
     if (milliseconds== false) {
       for (int i=0; i< samples; i++)  usTime[i] *= 1000.0;
     }
@@ -312,8 +312,10 @@ void mouseWheel(MouseEvent event) {
   if (mouseY>buttonY && mouseY <buttonY+buttonH &&
     mouseX>button4X && mouseX <button4X+smallButtonW) {
     //it is over the reducer button
+    xShift *= reducer;
     reducer-= wheel/10;
     reducer = constrain(reducer, 0.1, 9.9);
+    xShift /= reducer; // preserve scroll position
     getData();
   } else {        //move the graph
     xShift-=wheel*50;
@@ -393,7 +395,7 @@ void getData () {
   printArray(xTime);
   //println("pin: "+binary(changed[0], 6));
 
-  for (int i = 0; i < samples; i++) {  
+  for (int i = 0; i < samples; i++) {
     xTime[i] = usTime[i] / reducer;    //better to reduce the lenght of the x
   }
 
@@ -428,41 +430,41 @@ float[] spacing = {5, 8};  //used for the dashline function, pixels
 
 void dashline(float x0, float y0, float x1, float y1, float[] spacing) {
 
-  float distance = dist(x0, y0, x1, y1); 
-  float [ ] xSpacing = new float[spacing.length]; 
-  float [ ] ySpacing = new float[spacing.length]; 
-  float drawn = 0.0;  // amount of distance drawn 
+  float distance = dist(x0, y0, x1, y1);
+  float [ ] xSpacing = new float[spacing.length];
+  float [ ] ySpacing = new float[spacing.length];
+  float drawn = 0.0;  // amount of distance drawn
 
-  if (distance > 0) 
-  { 
-    int i; 
-    boolean drawLine = true; // alternate between dashes and gaps 
+  if (distance > 0)
+  {
+    int i;
+    boolean drawLine = true; // alternate between dashes and gaps
 
-    /* 
-     Figure out x and y distances for each of the spacing values 
-     I decided to trade memory for time; I'd rather allocate 
-     a few dozen bytes than have to do a calculation every time 
-     I draw. 
+    /*
+     Figure out x and y distances for each of the spacing values
+     I decided to trade memory for time; I'd rather allocate
+     a few dozen bytes than have to do a calculation every time
+     I draw.
      */
 
-    for (i = 0; i < spacing.length; i++) 
-    { 
-      xSpacing[i] = lerp(0, (x1 - x0), spacing[i] / distance); 
+    for (i = 0; i < spacing.length; i++)
+    {
+      xSpacing[i] = lerp(0, (x1 - x0), spacing[i] / distance);
       ySpacing[i] = lerp(0, (y1 - y0), spacing[i] / distance);
-    } 
+    }
 
-    i = 0; 
-    while (drawn < distance) 
-    { 
-      if (drawLine) 
-      { 
+    i = 0;
+    while (drawn < distance)
+    {
+      if (drawLine)
+      {
         line(x0, y0, x0 + xSpacing[i], y0 + ySpacing[i]);
-      } 
-      x0 += xSpacing[i]; 
-      y0 += ySpacing[i]; 
+      }
+      x0 += xSpacing[i];
+      y0 += ySpacing[i];
       /* Add distance "drawn" by this line or gap */
-      drawn = drawn + mag(xSpacing[i], ySpacing[i]); 
-      i = (i + 1) % spacing.length;  // cycle through array 
+      drawn = drawn + mag(xSpacing[i], ySpacing[i]);
+      i = (i + 1) % spacing.length;  // cycle through array
       drawLine = !drawLine;  // switch between dash and gap
     }
   }