Got it almost working...

src/graphics/Bitmap.cpp

@@ -22,6 +22,7 @@
 #include <algorithm>
 #include <spdlog/spdlog.h>
 
+#include <iostream>
 #include <iterator>
 #include <optional>
 #include <vector>
@@ -32,19 +33,20 @@ Bitmap<T>::Bitmap(uint16_t width, uint16_t height)
     : mWidth{width}, mHeight{height}, mPixels(width * height) {}
 
 template <class T>
-uint16_t Bitmap<T>::getWidth() {
+[[nodiscard]] uint16_t Bitmap<T>::getWidth() const {
     return mWidth;
 }
 
 template <class T>
-uint16_t Bitmap<T>::getHeight() {
+[[nodiscard]] uint16_t Bitmap<T>::getHeight() const {
     return mHeight;
 }
 
 template <class T>
 bool Bitmap<T>::setPixels(const std::vector<T>& pixels) {
     if (pixels.size() != mPixels.size()) {
-        spdlog::error("Invalid pixel buffer size.");
+        spdlog::error("Invalid pixel buffer size (got {} vs. {} bitmap size).", pixels.size(),
+                      mPixels.size());
         return false;
     }
 
@@ -53,12 +55,12 @@ bool Bitmap<T>::setPixels(const std::vector<T>& pixels) {
 }
 
 template <class T>
-std::vector<T> Bitmap<T>::getPixelsCpy() {
+[[nodiscard]] std::vector<T> Bitmap<T>::getPixelsCpy() const {
     return mPixels;
 }
 
 template <class T>
-std::optional<std::vector<T>> Bitmap<T>::getLine(uint16_t line) {
+[[nodiscard]] std::optional<std::vector<T>> Bitmap<T>::getLine(uint16_t line) const {
     if (line >= mHeight) {
         // out of bound
         return std::nullopt;
@@ -70,7 +72,7 @@ std::optional<std::vector<T>> Bitmap<T>::getLine(uint16_t line) {
 }
 
 template <class T>
-std::optional<std::vector<T>> Bitmap<T>::getCol(uint16_t col) {
+[[nodiscard]] std::optional<std::vector<T>> Bitmap<T>::getCol(uint16_t col) const {
     if (col >= mWidth) {
         // out of bound
         return std::nullopt;