Lots of updates:

1. Scrolling and click to set the cursor works.
2. GUI now uses Brass Mono as the font.
3. A lot of stability and other updates.

GapBuffer.cc

@@ -0,0 +1,203 @@
+#include "GapBuffer.h"
+
+#include <algorithm>
+#include <cassert>
+#include <cstring>
+
+GapBuffer::GapBuffer() = default;
+
+
+GapBuffer::GapBuffer(std::size_t initialCapacity)
+	: buffer_(nullptr), size_(0), capacity_(0)
+{
+	if (initialCapacity > 0) {
+		Reserve(initialCapacity);
+	}
+}
+
+
+GapBuffer::GapBuffer(const GapBuffer &other)
+	: buffer_(nullptr), size_(0), capacity_(0)
+{
+	if (other.capacity_ > 0) {
+		Reserve(other.capacity_);
+		if (other.size_ > 0) {
+			std::memcpy(buffer_, other.buffer_, other.size_);
+			size_ = other.size_;
+		}
+		setTerminator();
+	}
+}
+
+
+GapBuffer &
+GapBuffer::operator=(const GapBuffer &other)
+{
+	if (this == &other)
+		return *this;
+	if (other.capacity_ > capacity_) {
+		Reserve(other.capacity_);
+	}
+	if (other.size_ > 0) {
+		std::memcpy(buffer_, other.buffer_, other.size_);
+	}
+	size_ = other.size_;
+	setTerminator();
+	return *this;
+}
+
+
+GapBuffer::GapBuffer(GapBuffer &&other) noexcept
+	: buffer_(other.buffer_), size_(other.size_), capacity_(other.capacity_)
+{
+	other.buffer_   = nullptr;
+	other.size_     = 0;
+	other.capacity_ = 0;
+}
+
+
+GapBuffer &
+GapBuffer::operator=(GapBuffer &&other) noexcept
+{
+	if (this == &other)
+		return *this;
+	delete[] buffer_;
+	buffer_         = other.buffer_;
+	size_           = other.size_;
+	capacity_       = other.capacity_;
+	other.buffer_   = nullptr;
+	other.size_     = 0;
+	other.capacity_ = 0;
+	return *this;
+}
+
+
+GapBuffer::~GapBuffer()
+{
+	delete[] buffer_;
+}
+
+
+void
+GapBuffer::Reserve(const std::size_t newCapacity)
+{
+	if (newCapacity <= capacity_)
+		return;
+	// Allocate space for terminator as well
+	char *nb = new char[newCapacity + 1];
+	if (size_ > 0 && buffer_) {
+		std::memcpy(nb, buffer_, size_);
+	}
+	delete[] buffer_;
+	buffer_   = nb;
+	capacity_ = newCapacity;
+	setTerminator();
+}
+
+
+void
+GapBuffer::AppendChar(const char c)
+{
+	ensureCapacityFor(1);
+	buffer_[size_++] = c;
+	setTerminator();
+}
+
+
+void
+GapBuffer::Append(const char *s, const std::size_t len)
+{
+	if (!s || len == 0)
+		return;
+	ensureCapacityFor(len);
+	std::memcpy(buffer_ + size_, s, len);
+	size_ += len;
+	setTerminator();
+}
+
+
+void
+GapBuffer::Append(const GapBuffer &other)
+{
+	if (other.size_ == 0)
+		return;
+	Append(other.buffer_, other.size_);
+}
+
+
+void
+GapBuffer::PrependChar(char c)
+{
+	ensureCapacityFor(1);
+	// shift right by 1
+	if (size_ > 0) {
+		std::memmove(buffer_ + 1, buffer_, size_);
+	}
+	buffer_[0] = c;
+	++size_;
+	setTerminator();
+}
+
+
+void
+GapBuffer::Prepend(const char *s, std::size_t len)
+{
+	if (!s || len == 0)
+		return;
+	ensureCapacityFor(len);
+	if (size_ > 0) {
+		std::memmove(buffer_ + len, buffer_, size_);
+	}
+	std::memcpy(buffer_, s, len);
+	size_ += len;
+	setTerminator();
+}
+
+
+void
+GapBuffer::Prepend(const GapBuffer &other)
+{
+	if (other.size_ == 0)
+		return;
+	Prepend(other.buffer_, other.size_);
+}
+
+
+void
+GapBuffer::Clear()
+{
+	size_ = 0;
+	setTerminator();
+}
+
+
+void
+GapBuffer::ensureCapacityFor(std::size_t delta)
+{
+	if (capacity_ - size_ >= delta)
+		return;
+	auto required = size_ + delta;
+	Reserve(growCapacity(capacity_, required));
+}
+
+
+std::size_t
+GapBuffer::growCapacity(std::size_t current, std::size_t required)
+{
+	// geometric growth, at least required
+	std::size_t newCap = current ? current : 8;
+	while (newCap < required)
+		newCap = newCap + (newCap >> 1); // 1.5x growth
+	return newCap;
+}
+
+
+void
+GapBuffer::setTerminator() const
+{
+	if (!buffer_) {
+		return;
+	}
+
+	buffer_[size_] = '\0';
+}