Add helper functions to convert bitmap to different formats

Trex for now will keep using only 1-byte GRAY8 format as it provides all the information needed to render a glyph.

Emojis are not supported yet, unfortunately. They are more of a system thing rather than font.

closes #4

include/Trex/Atlas.hpp

@@ -22,8 +22,8 @@ namespace Trex
 
 	enum class RenderMode { DEFAULT, SDF, /* LCD */ };
 
-	using AtlasBitmap = std::vector<uint8_t>;
-	using AtlasGlyphs = std::map<uint32_t, Glyph>;
+	using AtlasBitmap = std::vector<uint8_t>; // 1-byte GRAYSCALE
+	using AtlasGlyphs = std::map<uint32_t, Glyph>; // key: glyph index in font (NOT codepoint!)
 
 	class Atlas
 	{

include/Trex/BitmapHelpers.hpp

@@ -0,0 +1,22 @@
+#pragma once
+#include <vector>
+#include <span>
+
+// Input to all these functions is always a 1-byte grayscale bitmap
+// Which means that each pixel is represented by a single byte where
+// value 0 means black and 255 means white.
+//
+// All conversion functions keep the grayscale value of the pixels.
+// Ondly the format of the bitmap is changed.
+
+namespace Trex
+{
+	// Convert 1-byte: GRAY8 to 2-byte: GRAYALPHA88
+	std::vector<uint8_t> ConvertToGrayAlpha(std::span<const uint8_t> input);
+
+	// Convert 1-byte: GRAY8 to 3-byte: RGB888
+	std::vector<uint8_t> ConvertToRGB(std::span<const uint8_t> input);
+
+	// Convert 1-byte: GRAY8 to 4-byte: RGBA8888
+	std::vector<uint8_t> ConvertToRGBA(std::span<const uint8_t> input);
+}

src/BitmapHelpers.cpp

@@ -0,0 +1,40 @@
+#include "Trex/BitmapHelpers.hpp"
+
+namespace Trex
+{
+	std::vector<uint8_t> ConvertToGrayAlpha(const std::span<const uint8_t> input)
+	{
+		std::vector<uint8_t> output(input.size() * 2);
+		for (size_t i = 0; i < input.size(); i++)
+		{
+			output[i * 2] = input[i];
+			output[i * 2 + 1] = 255;
+		}
+		return output;
+	}
+
+	std::vector<uint8_t> ConvertToRGB(const std::span<const uint8_t> input)
+	{
+		std::vector<uint8_t> output(input.size() * 3);
+		for (size_t i = 0; i < input.size(); i++)
+		{
+			output[i * 3] = input[i];
+			output[i * 3 + 1] = input[i];
+			output[i * 3 + 2] = input[i];
+		}
+		return output;
+	}
+
+	std::vector<uint8_t> ConvertToRGBA(const std::span<const uint8_t> input)
+	{
+		std::vector<uint8_t> output(input.size() * 4);
+		for (size_t i = 0; i < input.size(); i++)
+		{
+			output[i * 4] = input[i];
+			output[i * 4 + 1] = input[i];
+			output[i * 4 + 2] = input[i];
+			output[i * 4 + 3] = 255;
+		}
+		return output;
+	}
+}

tests/CMakeLists.txt

@@ -14,6 +14,7 @@ set(CMAKE_CXX_STANDARD 20)
 
 add_executable(${TEST_TARGET}
     TestAtlas.cpp
+    TestBitmapHelpers.cpp
     TestFont.cpp
     TestTextShaper.cpp
     TestCharset.cpp

tests/TestBitmapHelpers.cpp

@@ -0,0 +1,33 @@
+#include "Trex/BitmapHelpers.hpp"
+#include <gtest/gtest.h>
+#include <vector>
+
+struct BitmapHelpersTests : public ::testing::Test
+{
+	const std::vector<uint8_t> bitmap = {0, 127,
+										128, 255};
+};
+
+TEST_F(BitmapHelpersTests, ConvertToGrayAlpha)
+{
+	const std::vector<uint8_t> expected = {0, 255, 127, 255,
+										 128, 255, 255, 255};
+	const auto actual = Trex::ConvertToGrayAlpha(bitmap);
+	EXPECT_EQ(expected, actual);
+}
+
+TEST_F(BitmapHelpersTests, ConvertToRGB)
+{
+	const std::vector<uint8_t> expected = {0, 0, 0, 127, 127, 127,
+										 128, 128, 128, 255, 255, 255};
+	const auto actual = Trex::ConvertToRGB(bitmap);
+	EXPECT_EQ(expected, actual);
+}
+
+TEST_F(BitmapHelpersTests, ConvertToRGBA)
+{
+	const std::vector<uint8_t> expected = {0, 0, 0, 255, 127, 127, 127, 255,
+										 128, 128, 128, 255, 255, 255, 255, 255};
+	const auto actual = Trex::ConvertToRGBA(bitmap);
+	EXPECT_EQ(expected, actual);
+}