Add scrollbar to help window (#5481)

* Add scrollbar to help window. Also reduced the help window's text width to make space for the scrollbar.

Source/help.cpp

@@ -7,6 +7,7 @@
 #include <vector>
 
 #include "DiabloUI/ui_flags.hpp"
+#include "engine/render/clx_render.hpp"
 #include "engine/render/text_render.hpp"
 #include "init.h"
 #include "minitext.h"
@@ -101,7 +102,7 @@ constexpr int PaddingTop = 32;
 constexpr int PaddingLeft = 32;
 
 constexpr int PanelHeight = 297;
-constexpr int ContentTextWidth = 577;
+constexpr int ContentTextWidth = 565;
 
 int LineHeight()
 {
@@ -138,6 +139,29 @@ int NumVisibleLines()
 	return (ContentsTextHeight() - 1) / LineHeight() + 1; // Ceil
 }
 
+void DrawHelpSlider(const Surface &out)
+{
+	const Point uiPosition = GetUIRectangle().position;
+	const int sliderXPos = ContentTextWidth + uiPosition.x + 36;
+	const Point sliderPosition = uiPosition;
+	int sliderStart = uiPosition.y + HeaderHeight() + LineHeight() + 3;
+	int sliderEnd = uiPosition.y + PaddingTop + PanelHeight - 12;
+	ClxDraw(out, { sliderXPos, sliderStart }, (*pSTextSlidCels)[11]);
+	sliderStart += 12;
+	int sliderCurrent = sliderStart;
+	for (; sliderCurrent < sliderEnd; sliderCurrent += 12) {
+		ClxDraw(out, { sliderXPos, sliderCurrent }, (*pSTextSlidCels)[13]);
+	}
+	ClxDraw(out, { sliderXPos, sliderCurrent }, (*pSTextSlidCels)[10]);
+	// Subtract visible lines from the total number of lines to get the actual
+	// scroll range
+	const int scrollRange = HelpTextLines.size() - NumVisibleLines();
+	// Subtract the size of the arrow buttons to get the length of the interior
+	// part of the slider
+	const int sliderLength = sliderCurrent - 12 - sliderStart;
+	ClxDraw(out, { sliderXPos, sliderStart + ((SkipLines * sliderLength) / scrollRange) }, (*pSTextSlidCels)[12]);
+}
+
 } // namespace
 
 void InitHelp()
@@ -149,7 +173,7 @@ void InitHelp()
 	HelpFlag = false;
 
 	for (const auto *text : HelpText) {
-		const std::string paragraph = WordWrapString(_(text), 577);
+		const std::string paragraph = WordWrapString(_(text), ContentTextWidth);
 
 		size_t previous = 0;
 		while (true) {
@@ -210,6 +234,8 @@ void DrawHelp(const Surface &out)
 	DrawString(out, _("Press ESC to end or the arrow keys to scroll."),
 	    { { sx, contentY + ContentsTextHeight() + ContentPaddingY() + blankLineHeight }, { ContentTextWidth, lineHeight } },
 	    UiFlags::ColorWhitegold | UiFlags::AlignCenter);
+
+	DrawHelpSlider(out);
 }
 
 void DisplayHelp()