This took way too long. Zoom-box system works.

Base/Base.csproj.user

@@ -13,6 +13,9 @@
     <Compile Update="Forms\GraphForm.cs">
       <SubType>Form</SubType>
     </Compile>
+    <Compile Update="Forms\SetZoomForm.cs">
+      <SubType>Form</SubType>
+    </Compile>
     <Compile Update="Forms\TranslateForm.cs">
       <SubType>Form</SubType>
     </Compile>

Base/Forms/GraphForm.cs

@@ -21,6 +21,7 @@ public partial class GraphForm : Form
     public static readonly Color SemiAxisColor = Color.FromArgb(unchecked((int)0xFF_999999));
     public static readonly Color QuarterAxisColor = Color.FromArgb(unchecked((int)0xFF_E0E0E0));
     public static readonly Color UnitsTextColor = Color.Black;
+    public static readonly Color ZoomBoxColor = Color.Black;
 
     public Float2 ScreenCenter { get; private set; }
     public Float2 Dpi { get; private set; }
@@ -223,9 +224,8 @@ public partial class GraphForm : Form
 
         // Equation selection detection.
         // This system lets you select multiple graphs, and that's cool by me.
-        if (ableDrag)
+        if (selectState == SelectionState.GraphSelect)
         {
-            Font textFont = new(Font.Name, 8, FontStyle.Bold);
             for (int i = 0; i < ables.Count; i++)
             {
                 if (ables[i].ShouldSelectGraphable(this, graphMousePos, 2.5))
@@ -235,6 +235,20 @@ public partial class GraphForm : Form
                 }
             }
         }
+        else if (selectState == SelectionState.ZoomBox)
+        {
+            // Draw the current box selection.
+            Int2 boxPosA = GraphSpaceToScreenSpace(boxSelectA),
+                 boxPosB = GraphSpaceToScreenSpace(boxSelectB);
+
+            if (boxPosA.x > boxPosB.x) (boxPosA.x, boxPosB.x) = (boxPosB.x, boxPosA.x);
+            if (boxPosA.y > boxPosB.y) (boxPosA.y, boxPosB.y) = (boxPosB.y, boxPosA.y);
+
+            Pen boxPen = new(ZoomBoxColor, 2 * DpiFloat / 192);
+            g.DrawRectangle(boxPen, new(boxPosA.x, boxPosA.y,
+                                        boxPosB.x - boxPosA.x,
+                                        boxPosB.y - boxPosA.y));
+        }
 
         base.OnPaint(e);
     }
@@ -264,35 +278,52 @@ public partial class GraphForm : Form
                pixelPos.y >= 0 && pixelPos.y < ClientRectangle.Height;
     }
 
-    private bool mouseDrag = false;
+    private SelectionState selectState = SelectionState.None;
+    internal bool canBoxSelect;
+    private SetZoomForm? setZoomForm;
+
     private Int2 initialMouseLocation;
     private Float2 initialScreenCenter;
 
-    private bool ableDrag = false;
+    private Float2 boxSelectA, boxSelectB;
+
     protected override void OnMouseDown(MouseEventArgs e)
     {
-        if (!mouseDrag)
+        if (selectState == SelectionState.None && canBoxSelect)
+        {
+            Point clientMousePos = PointToClient(Cursor.Position);
+            Float2 graphMousePos = ScreenSpaceToGraphSpace(new(clientMousePos.X,
+                                                               clientMousePos.Y));
+
+            boxSelectA = graphMousePos;
+            boxSelectB = graphMousePos;
+
+            selectState = SelectionState.ZoomBox;
+        }
+
+        if (selectState == SelectionState.None)
         {
             Point clientMousePos = PointToClient(Cursor.Position);
             Float2 graphMousePos = ScreenSpaceToGraphSpace(new(clientMousePos.X,
                                                                clientMousePos.Y));
             foreach (Graphable able in Graphables)
             {
-                if (able.ShouldSelectGraphable(this, graphMousePos, 1)) ableDrag = true;
+                if (able.ShouldSelectGraphable(this, graphMousePos, 1))
+                    selectState = SelectionState.GraphSelect;
             }
-            if (ableDrag) Invalidate(false);
+            if (selectState == SelectionState.GraphSelect) Invalidate(false);
         }
 
-        if (!ableDrag)
+        if (selectState == SelectionState.None)
         {
-            mouseDrag = true;
+            selectState = SelectionState.ViewportDrag;
             initialMouseLocation = new Int2(Cursor.Position.X, Cursor.Position.Y);
             initialScreenCenter = ScreenCenter;
         }
     }
     protected override void OnMouseUp(MouseEventArgs e)
     {
-        if (mouseDrag)
+        if (selectState == SelectionState.ViewportDrag)
         {
             Int2 pixelDiff = new(initialMouseLocation.x - Cursor.Position.X,
                              initialMouseLocation.y - Cursor.Position.Y);
@@ -300,22 +331,52 @@ public partial class GraphForm : Form
             ScreenCenter = new(initialScreenCenter.x + graphDiff.x,
                                initialScreenCenter.y + graphDiff.y);
         }
-        mouseDrag = false;
+        else if (selectState == SelectionState.ZoomBox)
-        ableDrag = false;
+        {
+            Point clientMousePos = PointToClient(Cursor.Position);
+            Float2 graphMousePos = ScreenSpaceToGraphSpace(new(clientMousePos.X,
+                                                               clientMousePos.Y));
+            boxSelectB = graphMousePos;
+
+            // Set center.
+            ScreenCenter = new((boxSelectA.x + boxSelectB.x) * 0.5,
+                              -(boxSelectA.y + boxSelectB.y) * 0.5);
+
+            // Set zoom. Kind of weird but it works.
+            Float2 minGraph = MinVisibleGraph, maxGraph = MaxVisibleGraph;
+            Float2 oldDist = new(maxGraph.x - minGraph.x,
+                                 maxGraph.y - minGraph.y);
+            Float2 newDist = new(Math.Abs(boxSelectB.x - boxSelectA.x),
+                                 Math.Abs(boxSelectB.y - boxSelectA.y));
+            ZoomLevel = new(ZoomLevel.x * newDist.x / oldDist.x,
+                            ZoomLevel.y * newDist.y / oldDist.y);
+
+            setZoomForm!.CompleteBoxSelection();
+
+            boxSelectA = new(0, 0);
+            boxSelectB = new(0, 0);
+        }
+        selectState = SelectionState.None;
         Invalidate(false);
     }
     protected override void OnMouseMove(MouseEventArgs e)
     {
-        if (mouseDrag)
+        if (selectState == SelectionState.ViewportDrag)
         {
             Int2 pixelDiff = new(initialMouseLocation.x - Cursor.Position.X,
                              initialMouseLocation.y - Cursor.Position.Y);
             Float2 graphDiff = new(pixelDiff.x * ZoomLevel.x / Dpi.x, pixelDiff.y * ZoomLevel.y / Dpi.y);
             ScreenCenter = new(initialScreenCenter.x + graphDiff.x,
                                initialScreenCenter.y + graphDiff.y);
-            Invalidate(false);
         }
-        else if (ableDrag) Invalidate(false);
+        else if (selectState == SelectionState.ZoomBox)
+        {
+            Point clientMousePos = PointToClient(Cursor.Position);
+            Float2 graphMousePos = ScreenSpaceToGraphSpace(new(clientMousePos.X,
+                                                               clientMousePos.Y));
+            boxSelectB = graphMousePos;
+        }
+        Invalidate(false);
     }
     protected override void OnMouseWheel(MouseEventArgs e)
     {
@@ -445,7 +506,31 @@ public partial class GraphForm : Form
 
     private void ButtonViewportSetZoom_Click(object? sender, EventArgs e)
     {
-        MessageBox.Show("TODO", "Set Viewport Zoom", MessageBoxButtons.OK, MessageBoxIcon.Error);
+        if (setZoomForm is not null)
+        {
+            setZoomForm.Focus();
+            return;
+        }
+
+        SetZoomForm zoomForm = new(this)
+        {
+            StartPosition = FormStartPosition.Manual,
+        };
+        zoomForm.Location = new Point(Location.X + ClientRectangle.Width + 10,
+                                    Location.Y + (ClientRectangle.Height - zoomForm.ClientRectangle.Height) / 2);
+
+        if (zoomForm.Location.X + zoomForm.Width > Screen.FromControl(this).WorkingArea.Width)
+        {
+            zoomForm.StartPosition = FormStartPosition.WindowsDefaultLocation;
+        }
+
+        setZoomForm = zoomForm;
+        zoomForm.Show();
+        zoomForm.FormClosing += (o, e) =>
+        {
+            zoomForm.CompleteBoxSelection();
+            setZoomForm = null;
+        };
     }
     private void ButtonViewportSetCenter_Click(object? sender, EventArgs e)
     {
@@ -464,12 +549,20 @@ public partial class GraphForm : Form
         WindowState = FormWindowState.Normal;
     }
 
+    private ViewCacheForm? cacheForm;
     private void MenuMiscCaches_Click(object? sender, EventArgs e)
     {
+        if (this.cacheForm is not null)
+        {
+            this.cacheForm.Focus();
+            return;
+        }
+
         ViewCacheForm cacheForm = new(this)
         {
             StartPosition = FormStartPosition.Manual
         };
+        this.cacheForm = cacheForm;
 
         cacheForm.Location = new Point(Location.X + ClientRectangle.Width + 10,
                                        Location.Y + (ClientRectangle.Height - cacheForm.ClientRectangle.Height) / 2);
@@ -594,4 +687,12 @@ public partial class GraphForm : Form
             Console.WriteLine($"Failed to check for updates:\n{ex}");
         }
     }
+
+    private enum SelectionState
+    {
+        None = 0,
+        ViewportDrag,
+        GraphSelect,
+        ZoomBox,
+    }
 }

Base/Forms/SetZoomForm.Designer.cs

@@ -0,0 +1,60 @@
+namespace Graphing.Forms
+{
+    partial class SetZoomForm
+    {
+        /// <summary>
+        /// Required designer variable.
+        /// </summary>
+        private System.ComponentModel.IContainer components = null;
+
+        /// <summary>
+        /// Clean up any resources being used.
+        /// </summary>
+        /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
+        protected override void Dispose(bool disposing)
+        {
+            if (disposing && (components != null))
+            {
+                components.Dispose();
+            }
+            base.Dispose(disposing);
+        }
+
+        #region Windows Form Designer generated code
+
+        /// <summary>
+        /// Required method for Designer support - do not modify
+        /// the contents of this method with the code editor.
+        /// </summary>
+        private void InitializeComponent()
+        {
+            EnableBoxSelect = new System.Windows.Forms.Button();
+            SuspendLayout();
+            // 
+            // EnableBoxSelect
+            // 
+            EnableBoxSelect.Location = new System.Drawing.Point(12, 12);
+            EnableBoxSelect.Name = "EnableBoxSelect";
+            EnableBoxSelect.Size = new System.Drawing.Size(150, 46);
+            EnableBoxSelect.TabIndex = 0;
+            EnableBoxSelect.Text = "Box Select";
+            EnableBoxSelect.UseVisualStyleBackColor = true;
+            EnableBoxSelect.Click += EnableBoxSelect_Click;
+            // 
+            // SetZoomForm
+            // 
+            AutoScaleDimensions = new System.Drawing.SizeF(13F, 32F);
+            AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
+            ClientSize = new System.Drawing.Size(800, 450);
+            Controls.Add(EnableBoxSelect);
+            FormBorderStyle = System.Windows.Forms.FormBorderStyle.FixedToolWindow;
+            Name = "SetZoomForm";
+            Text = "Set Viewport Zoom";
+            ResumeLayout(false);
+        }
+
+        #endregion
+
+        private System.Windows.Forms.Button EnableBoxSelect;
+    }
+}

Base/Forms/SetZoomForm.cs

@@ -0,0 +1,38 @@
+using System;
+using System.Windows.Forms;
+
+namespace Graphing.Forms;
+
+public partial class SetZoomForm : Form
+{
+    private readonly GraphForm refForm;
+
+    private bool boxSelectEnabled;
+
+    public SetZoomForm(GraphForm refForm)
+    {
+        InitializeComponent();
+        this.refForm = refForm;
+    }
+
+    private void EnableBoxSelect_Click(object? sender, EventArgs e)
+    {
+        boxSelectEnabled = !boxSelectEnabled;
+        refForm.canBoxSelect = boxSelectEnabled;
+
+        if (boxSelectEnabled)
+        {
+            EnableBoxSelect.Text = $"Cancel ...";
+            refForm.Focus();
+        }
+        else
+        {
+            EnableBoxSelect.Text = "Box Select";
+        }
+    }
+
+    internal void CompleteBoxSelection()
+    {
+        if (boxSelectEnabled) EnableBoxSelect_Click(null, new());
+    }
+}

Base/Forms/SetZoomForm.resx

@@ -0,0 +1,120 @@
+<?xml version="1.0" encoding="utf-8"?>
+<root>
+  <!--
+    Microsoft ResX Schema 
+
+    Version 2.0
+
+    The primary goals of this format is to allow a simple XML format
+    that is mostly human readable. The generation and parsing of the
+    various data types are done through the TypeConverter classes
+    associated with the data types.
+
+    Example:
+
+    ... ado.net/XML headers & schema ...
+    <resheader name="resmimetype">text/microsoft-resx</resheader>
+    <resheader name="version">2.0</resheader>
+    <resheader name="reader">System.Resources.ResXResourceReader, System.Windows.Forms, ...</resheader>
+    <resheader name="writer">System.Resources.ResXResourceWriter, System.Windows.Forms, ...</resheader>
+    <data name="Name1"><value>this is my long string</value><comment>this is a comment</comment></data>
+    <data name="Color1" type="System.Drawing.Color, System.Drawing">Blue</data>
+    <data name="Bitmap1" mimetype="application/x-microsoft.net.object.binary.base64">
+        <value>[base64 mime encoded serialized .NET Framework object]</value>
+    </data>
+    <data name="Icon1" type="System.Drawing.Icon, System.Drawing" mimetype="application/x-microsoft.net.object.bytearray.base64">
+        <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>
+        <comment>This is a comment</comment>
+    </data>
+
+    There are any number of "resheader" rows that contain simple
+    name/value pairs.
+
+    Each data row contains a name, and value. The row also contains a
+    type or mimetype. Type corresponds to a .NET class that support
+    text/value conversion through the TypeConverter architecture.
+    Classes that don't support this are serialized and stored with the
+    mimetype set.
+
+    The mimetype is used for serialized objects, and tells the
+    ResXResourceReader how to depersist the object. This is currently not
+    extensible. For a given mimetype the value must be set accordingly:
+
+    Note - application/x-microsoft.net.object.binary.base64 is the format
+    that the ResXResourceWriter will generate, however the reader can
+    read any of the formats listed below.
+
+    mimetype: application/x-microsoft.net.object.binary.base64
+    value   : The object must be serialized with
+            : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter
+            : and then encoded with base64 encoding.
+    
+    mimetype: application/x-microsoft.net.object.soap.base64
+    value   : The object must be serialized with
+            : System.Runtime.Serialization.Formatters.Soap.SoapFormatter
+            : and then encoded with base64 encoding.
+
+    mimetype: application/x-microsoft.net.object.bytearray.base64
+    value   : The object must be serialized into a byte array
+            : using a System.ComponentModel.TypeConverter
+            : and then encoded with base64 encoding.
+    -->
+  <xsd:schema id="root" xmlns="" xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata">
+    <xsd:import namespace="http://www.w3.org/XML/1998/namespace" />
+    <xsd:element name="root" msdata:IsDataSet="true">
+      <xsd:complexType>
+        <xsd:choice maxOccurs="unbounded">
+          <xsd:element name="metadata">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" />
+              </xsd:sequence>
+              <xsd:attribute name="name" use="required" type="xsd:string" />
+              <xsd:attribute name="type" type="xsd:string" />
+              <xsd:attribute name="mimetype" type="xsd:string" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="assembly">
+            <xsd:complexType>
+              <xsd:attribute name="alias" type="xsd:string" />
+              <xsd:attribute name="name" type="xsd:string" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="data">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+                <xsd:element name="comment" type="xsd:string" minOccurs="0" msdata:Ordinal="2" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" msdata:Ordinal="1" />
+              <xsd:attribute name="type" type="xsd:string" msdata:Ordinal="3" />
+              <xsd:attribute name="mimetype" type="xsd:string" msdata:Ordinal="4" />
+              <xsd:attribute ref="xml:space" />
+            </xsd:complexType>
+          </xsd:element>
+          <xsd:element name="resheader">
+            <xsd:complexType>
+              <xsd:sequence>
+                <xsd:element name="value" type="xsd:string" minOccurs="0" msdata:Ordinal="1" />
+              </xsd:sequence>
+              <xsd:attribute name="name" type="xsd:string" use="required" />
+            </xsd:complexType>
+          </xsd:element>
+        </xsd:choice>
+      </xsd:complexType>
+    </xsd:element>
+  </xsd:schema>
+  <resheader name="resmimetype">
+    <value>text/microsoft-resx</value>
+  </resheader>
+  <resheader name="version">
+    <value>2.0</value>
+  </resheader>
+  <resheader name="reader">
+    <value>System.Resources.ResXResourceReader, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+  <resheader name="writer">
+    <value>System.Resources.ResXResourceWriter, System.Windows.Forms, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089</value>
+  </resheader>
+</root>