Add some functions to generate images

Namely:
- GenImageHorizontalV
- GenImageHorizontalH
- GenImageChecked
- GenImageWhiteNoise
- GenImageCellular

The gradient implementation may be a bit naive, for example it doesn't do any gamma correction.

examples/textures/textures_image_generation.c

@@ -0,0 +1,57 @@
+/*******************************************************************************************
+*
+*   raylib [textures] example - Procedural images generation
+*
+*   This example has been created using raylib 1.7 (www.raylib.com)
+*   raylib is licensed under an unmodified zlib/libpng license (View raylib.h for details)
+*
+*   Copyright (c) 2O17 Ramon Santamaria (@raysan5)
+*
+********************************************************************************************/
+
+#include "raylib.h"
+
+#define TEXTURES_NUM 5 // for now we have 5 generation algorithms
+
+int main()
+{
+    int screenWidth = 800;
+    int screenHeight = 450;
+
+    InitWindow(screenWidth, screenHeight, "raylib [textures] example - procedural images generation");
+
+    Image verticalGradient = GenImageGradientV(screenWidth, screenHeight, RED, BLUE);
+    Image horizontalGradient = GenImageGradientH(screenWidth, screenHeight, RED, BLUE);
+    Image checked = GenImageChecked(screenWidth, screenHeight, 32, 32, RED, BLUE);
+    Image whiteNoise = GenImageWhiteNoise(screenWidth, screenHeight, 0.5f);
+    Image cellular = GenImageCellular(screenWidth, screenHeight, 32);
+
+    Texture2D textures[TEXTURES_NUM];
+    textures[0] = LoadTextureFromImage(verticalGradient);
+    textures[1] = LoadTextureFromImage(horizontalGradient);
+    textures[2] = LoadTextureFromImage(checked);
+    textures[3] = LoadTextureFromImage(whiteNoise);
+    textures[4] = LoadTextureFromImage(cellular);
+
+    int currentTexture = 0;
+
+    while (!WindowShouldClose())
+    {
+        if (IsMouseButtonPressed(MOUSE_LEFT_BUTTON))
+        {
+            currentTexture = (currentTexture + 1) % TEXTURES_NUM; // cycle between the 5 textures
+        }
+
+        BeginDrawing();
+            ClearBackground(RAYWHITE);
+            DrawTexture(textures[currentTexture], 0, 0, WHITE);
+        EndDrawing();
+    }
+
+    for (int i = 0; i < TEXTURES_NUM; i++) // unload the textures
+    {
+        UnloadTexture(textures[i]);
+    }
+
+    CloseWindow();
+}

src/raylib.h

@@ -873,6 +873,13 @@ RLAPI void ImageColorGrayscale(Image *image);
 RLAPI void ImageColorContrast(Image *image, float contrast);                                             // Modify image color: contrast (-100 to 100)
 RLAPI void ImageColorBrightness(Image *image, int brightness);                                           // Modify image color: brightness (-255 to 255)
 
+// Image generation functions
+RLAPI Image GenImageGradientV(int width, int height, Color top, Color bottom);                           // Generate image: vertical gradient
+RLAPI Image GenImageGradientH(int width, int height, Color left, Color right);                           // Generate image: horizontal gradient
+RLAPI Image GenImageChecked(int width, int height, int checksX, int checksY, Color col1, Color col2);    // Generate image: checked
+RLAPI Image GenImageWhiteNoise(int width, int height, float factor);                                     // Generate image: white noise
+RLAPI Image GenImageCellular(int width, int height, int tileSize);                                       // Generate image: cellular algorithm. Bigger tileSize means bigger cells
+
 // Texture2D configuration functions
 RLAPI void GenTextureMipmaps(Texture2D *texture);                                                        // Generate GPU mipmaps for a texture
 RLAPI void SetTextureFilter(Texture2D texture, int filterMode);                                          // Set texture scaling filter mode

src/textures.c

@@ -1431,6 +1431,148 @@ void ImageColorBrightness(Image *image, int brightness)
 }
 #endif      // SUPPORT_IMAGE_MANIPULATION
 
+// Generate image: vertical gradient
+Image GenImageGradientV(int width, int height, Color top, Color bottom)
+{
+    Color *pixels = (Color *)malloc(width*height*sizeof(Color));
+
+    for (int j = 0; j < height; j++)
+    {
+        float factor = (float)j / (float)height;
+        for (int i = 0; i < width; i++)
+        {
+            pixels[j*width + i].r = (int)((float)bottom.r * factor + (float)top.r * (1.f - factor));
+            pixels[j*width + i].g = (int)((float)bottom.g * factor + (float)top.g * (1.f - factor));
+            pixels[j*width + i].b = (int)((float)bottom.b * factor + (float)top.b * (1.f - factor));
+            pixels[j*width + i].a = (int)((float)bottom.a * factor + (float)top.a * (1.f - factor));
+        }
+    }
+
+    Image image = LoadImageEx(pixels, width, height);
+    free(pixels);
+
+    return image;
+}
+
+// Generate image: horizontal gradient
+Image GenImageGradientH(int width, int height, Color left, Color right)
+{
+    Color *pixels = (Color *)malloc(width*height*sizeof(Color));
+
+    for (int i = 0; i < width; i++)
+    {
+        float factor = (float)i / (float)width;
+        for (int j = 0; j < height; j++)
+        {
+            pixels[j*width + i].r = (int)((float)right.r * factor + (float)left.r * (1.f - factor));
+            pixels[j*width + i].g = (int)((float)right.g * factor + (float)left.g * (1.f - factor));
+            pixels[j*width + i].b = (int)((float)right.b * factor + (float)left.b * (1.f - factor));
+            pixels[j*width + i].a = (int)((float)right.a * factor + (float)left.a * (1.f - factor));
+        }
+    }
+
+    Image image = LoadImageEx(pixels, width, height);
+    free(pixels);
+
+    return image;
+}
+
+// Generate image: checked
+Image GenImageChecked(int width, int height, int checksX, int checksY, Color col1, Color col2)
+{
+    Color *pixels = (Color *)malloc(width*height*sizeof(Color));
+
+    for (int y = 0; y < height; y++)
+    {
+        for (int x = 0; x < width; x++)
+        {
+            if ((x/checksX + y/checksY) % 2 == 0) pixels[y*width + x] = col1;
+            else pixels[y*width + x] = col2;
+        }
+    }
+
+    Image image = LoadImageEx(pixels, width, height);
+    free(pixels);
+
+    return image;
+}
+
+// Generate image: white noise
+Image GenImageWhiteNoise(int width, int height, float factor)
+{
+    Color *pixels = (Color *)malloc(width*height*sizeof(Color));
+
+    for (int i = 0; i < width*height; i++)
+    {
+        if (GetRandomValue(0, 99) < (int)(factor * 100.f)) pixels[i] = WHITE;
+        else pixels[i] = BLACK;
+    }
+
+    Image image = LoadImageEx(pixels, width, height);
+    free(pixels);
+
+    return image;
+}
+
+// Generate image: cellular algorithm. Bigger tileSize means bigger cells
+Image GenImageCellular(int width, int height, int tileSize)
+{
+    Color *pixels = (Color*)malloc(width*height*sizeof(Color));
+
+    int seeds_per_row = width / tileSize;
+    int seeds_per_col = height / tileSize;
+    int seeds_count = seeds_per_row * seeds_per_col;
+
+    Vector2* seeds = (Vector2*)malloc(seeds_count * sizeof(Vector2));
+
+    for (int i = 0; i < seeds_count; i++)
+    {
+        int y = (i / seeds_per_row) * tileSize + GetRandomValue(0, tileSize-1);
+        int x = (i % seeds_per_row) * tileSize + GetRandomValue(0, tileSize-1);
+        seeds[i] = (Vector2){x, y};
+    }
+
+    for (int y = 0; y < height; y++)
+    {
+        int tile_y = y / tileSize;
+        for (int x = 0; x < width; x++)
+        {
+            int tile_x = x / tileSize;
+
+            float min_distance = strtod("Inf", NULL);
+
+            // Check all adjacent tiles
+            for (int i = -1; i < 2; i++)
+            {
+                if (tile_x + i < 0 || tile_x + i >= seeds_per_row) continue;
+
+                for (int j = -1; j < 2; j++)
+                {
+                    if (tile_y + j < 0 || tile_y + j >= seeds_per_col) continue;
+
+                    Vector2 neighbor_seed = seeds[(tile_y+j) * seeds_per_row + tile_x+i];
+
+                    float dist = hypot(x - (int)neighbor_seed.x, y - (int)neighbor_seed.y);
+                    min_distance = fmin(min_distance, dist);
+                }
+            }
+
+            // I made this up but it seems to give good results at all tile sizes
+            int intensity = (int)(min_distance * 256.f / tileSize);
+            if (intensity > 255) intensity = 255;
+
+            Color c = {intensity, intensity, intensity, 255};
+            pixels[y*width + x] = c;
+        }
+    }
+    free(seeds);
+
+    Image image = LoadImageEx(pixels, width, height);
+    free(pixels);
+
+    return image;
+}
+
 // Generate GPU mipmaps for a texture
 void GenTextureMipmaps(Texture2D *texture)
 {