[rtextures] Created ImageFromChannel() (#4105)

* created ImageFromChannel

Adds the possibility to extract a specific channel from an image

* naming convention

* example window height

* removed threshold

* removed alpha channel

* channel example organization

* updated channel example image

examples/textures/textures_image_channel.c

@@ -0,0 +1,106 @@
+/*******************************************************************************************
+*
+*   raylib [textures] example - Retrive image channel (mask)
+*
+*   NOTE: Images are loaded in CPU memory (RAM); textures are loaded in GPU memory (VRAM)
+*
+*   Example originally created with raylib 5.1-dev, last time updated with raylib 5.1-dev
+*
+*   Example contributed by Bruno Cabral (github.com/brccabral) and reviewed by Ramon Santamaria (@raysan5)
+*
+*   Example licensed under an unmodified zlib/libpng license, which is an OSI-certified,
+*   BSD-like license that allows static linking with closed source software
+*
+*   Copyright (c) 2024-2024 Bruno Cabral (github.com/brccabral) and Ramon Santamaria (@raysan5)
+*
+********************************************************************************************/
+
+#include <raylib.h>
+
+//------------------------------------------------------------------------------------
+// Program main entry point
+//------------------------------------------------------------------------------------
+int main(void)
+{
+    // Initialization
+    //--------------------------------------------------------------------------------------
+
+    const int screenWidth = 800;
+    const int screenHeight = 450;
+
+    InitWindow(screenWidth, screenHeight, "raylib [textures] example - extract channel from image");
+
+    Image fudesumiImage = LoadImage("resources/fudesumi.png");
+
+    Image imageAlpha = ImageFromChannel(fudesumiImage, 3);
+    ImageAlphaMask(&imageAlpha, imageAlpha);
+
+    Image imageRed = ImageFromChannel(fudesumiImage, 0);
+    ImageAlphaMask(&imageRed, imageAlpha);
+
+    Image imageGreen = ImageFromChannel(fudesumiImage, 1);
+    ImageAlphaMask(&imageGreen, imageAlpha);
+
+    Image imageBlue = ImageFromChannel(fudesumiImage, 2);
+    ImageAlphaMask(&imageBlue, imageAlpha);
+
+    Image backgroundImage = GenImageChecked(screenWidth, screenHeight, screenWidth/20, screenHeight/20, ORANGE, YELLOW);
+
+    Texture2D fudesumiTexture = LoadTextureFromImage(fudesumiImage);
+    Texture2D textureAlpha = LoadTextureFromImage(imageAlpha);
+    Texture2D textureRed = LoadTextureFromImage(imageRed);
+    Texture2D textureGreen = LoadTextureFromImage(imageGreen);
+    Texture2D textureBlue = LoadTextureFromImage(imageBlue);
+    Texture2D backgroundTexture = LoadTextureFromImage(backgroundImage);
+
+    UnloadImage(fudesumiImage);
+    UnloadImage(imageAlpha);
+    UnloadImage(imageRed);
+    UnloadImage(imageGreen);
+    UnloadImage(imageBlue);
+    UnloadImage(backgroundImage);
+
+    SetTargetFPS(60);               // Set our game to run at 60 frames-per-second
+
+    Rectangle fudesumiRec = {0, 0, fudesumiImage.width, fudesumiImage.height};
+
+    Rectangle fudesumiPos = {50, 10, fudesumiImage.width*0.8f, fudesumiImage.height*0.8f};
+    Rectangle redPos = { 410, 10, fudesumiPos.width / 2, fudesumiPos.height / 2 };
+    Rectangle greenPos = { 600, 10, fudesumiPos.width / 2, fudesumiPos.height / 2 };
+    Rectangle bluePos = { 410, 230, fudesumiPos.width / 2, fudesumiPos.height / 2 };
+    Rectangle alphaPos = { 600, 230, fudesumiPos.width / 2, fudesumiPos.height / 2 };
+
+    //--------------------------------------------------------------------------------------
+
+    // Main game loop
+    while (!WindowShouldClose())    // Detect window close button or ESC key
+    {
+        // Draw
+        //----------------------------------------------------------------------------------
+        BeginDrawing();
+
+            DrawTexture(backgroundTexture, 0, 0, WHITE);
+            DrawTexturePro(fudesumiTexture, fudesumiRec, fudesumiPos, (Vector2) {0, 0}, 0, WHITE);
+
+            DrawTexturePro(textureRed, fudesumiRec, redPos, (Vector2) {0, 0}, 0, RED);
+            DrawTexturePro(textureGreen, fudesumiRec, greenPos, (Vector2) {0, 0}, 0, GREEN);
+            DrawTexturePro(textureBlue, fudesumiRec, bluePos, (Vector2) {0, 0}, 0, BLUE);
+            DrawTexturePro(textureAlpha, fudesumiRec, alphaPos, (Vector2) {0, 0}, 0, WHITE);
+
+        EndDrawing();
+        //----------------------------------------------------------------------------------
+    }
+
+    // De-Initialization
+    //--------------------------------------------------------------------------------------
+    UnloadTexture(backgroundTexture);
+    UnloadTexture(fudesumiTexture);
+    UnloadTexture(textureRed);
+    UnloadTexture(textureGreen);
+    UnloadTexture(textureBlue);
+    UnloadTexture(textureAlpha);
+    CloseWindow();        // Close window and OpenGL context
+    //--------------------------------------------------------------------------------------
+
+    return 0;
+}