Adding basic palette-switching example using uniform arrays.

examples/CMakeLists.txt

@@ -52,6 +52,7 @@ if(${PLATFORM} MATCHES "Android")
   list(REMOVE_ITEM example_sources ${CMAKE_CURRENT_SOURCE_DIR}/shaders/shaders_model_shader.c)
   list(REMOVE_ITEM example_sources ${CMAKE_CURRENT_SOURCE_DIR}/shaders/shaders_postprocessing.c)
   list(REMOVE_ITEM example_sources ${CMAKE_CURRENT_SOURCE_DIR}/shaders/shaders_raymarching.c)
+  list(REMOVE_ITEM example_sources ${CMAKE_CURRENT_SOURCE_DIR}/shaders/shaders_palette_switch.c)
 
 elseif(${PLATFORM} MATCHES "Web")
   set(CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -Os -s USE_GLFW=3 -s ASSERTIONS=1 -s WASM=1 -s EMTERPRETIFY=1 -s EMTERPRETIFY_ASYNC=1")

examples/Makefile

@@ -420,6 +420,7 @@ EXAMPLES = \
     shaders/shaders_custom_uniform \
     shaders/shaders_postprocessing \
     shaders/shaders_raymarching \
+    shaders/shaders_palette_switch \
     audio/audio_sound_loading \
     audio/audio_music_stream \
     audio/audio_module_playing \

examples/shaders/resources/shaders/glsl100/palette-switch.fs

@@ -0,0 +1,29 @@
+#version 100
+
+precision mediump float;
+
+const int colors = 8;
+
+// Input vertex attributes (from vertex shader)
+varying vec2 fragTexCoord;
+varying vec4 fragColor;
+
+// Input uniform values
+uniform sampler2D texture0;
+uniform ivec3 palette[colors];
+
+void main()
+{
+    // Texel color fetching from texture sampler
+    vec4 texelColor = texture(texture0, fragTexCoord) * fragColor;
+
+    // Convert the (normalized) texel color RED component (GB would work, too)
+    // to the palette index by scaling up from [0, 1] to [0, 255].
+    int index = int(texelColor.r * 255.0);
+    ivec3 color = palette[index];
+
+    // Calculate final fragment color. Note that the palette color components
+    // are defined in the range [0, 255] and need to be normalized to [0, 1]
+    // for OpenGL to work.
+    gl_FragColor = vec4(color / 255.0, texelColor.a);
+}

examples/shaders/resources/shaders/glsl120/palette-switch.fs

@@ -0,0 +1,27 @@
+#version 120
+
+const int colors = 8;
+
+// Input fragment attributes (from fragment shader)
+varying vec2 fragTexCoord;
+varying vec4 fragColor;
+
+// Input uniform values
+uniform sampler2D texture0;
+uniform ivec3 palette[colors];
+
+void main()
+{
+    // Texel color fetching from texture sampler
+    vec4 texelColor = texture(texture0, fragTexCoord) * fragColor;
+
+    // Convert the (normalized) texel color RED component (GB would work, too)
+    // to the palette index by scaling up from [0, 1] to [0, 255].
+    int index = int(texelColor.r * 255.0);
+    ivec3 color = palette[index];
+
+    // Calculate final fragment color. Note that the palette color components
+    // are defined in the range [0, 255] and need to be normalized to [0, 1]
+    // for OpenGL to work.
+    gl_FragColor = vec4(color / 255.0, texelColor.a);
+}

examples/shaders/resources/shaders/glsl330/palette-switch.fs

@@ -0,0 +1,30 @@
+#version 330
+
+const int colors = 8;
+
+// Input fragment attributes (from fragment shader)
+in vec2 fragTexCoord;
+in vec4 fragColor;
+
+// Input uniform values
+uniform sampler2D texture0;
+uniform ivec3 palette[colors];
+
+// Output fragment color
+out vec4 finalColor;
+
+void main()
+{
+    // Texel color fetching from texture sampler
+    vec4 texelColor = texture(texture0, fragTexCoord) * fragColor;
+
+    // Convert the (normalized) texel color RED component (GB would work, too)
+    // to the palette index by scaling up from [0, 1] to [0, 255].
+    int index = int(texelColor.r * 255.0);
+    ivec3 color = palette[index];
+
+    // Calculate final fragment color. Note that the palette color components
+    // are defined in the range [0, 255] and need to be normalized to [0, 1]
+    // for OpenGL to work.
+    finalColor = vec4(color / 255.0, texelColor.a);
+}

examples/shaders/shaders_palette_switch.c

@@ -0,0 +1,160 @@
+/*******************************************************************************************
+*
+*   raylib [shaders] example - Apply a postprocessing shader to a scene
+*
+*   NOTE: This example requires raylib OpenGL 3.3 or ES2 versions for shaders support,
+*         OpenGL 1.1 does not support shaders, recompile raylib to OpenGL 3.3 version.
+*
+*   NOTE: Shaders used in this example are #version 330 (OpenGL 3.3), to test this example
+*         on OpenGL ES 2.0 platforms (Android, Raspberry Pi, HTML5), use #version 100 shaders
+*         raylib comes with shaders ready for both versions, check raylib/shaders install folder
+*
+*   This example has been created using raylib 2.x (www.raylib.com)
+*   raylib is licensed under an unmodified zlib/libpng license (View raylib.h for details)
+*
+*   Copyright (c) 2015 Ramon Santamaria (@raysan5)
+*
+********************************************************************************************/
+
+#include "raylib.h"
+
+#if defined(PLATFORM_DESKTOP)
+    #define GLSL_VERSION            330
+#else   // PLATFORM_RPI, PLATFORM_ANDROID, PLATFORM_WEB
+    #define GLSL_VERSION            100
+#endif
+
+#define MAX_PALETTES            3
+#define COLORS_PER_PALETTE      8
+#define VALUES_PER_COLOR        3
+
+static const int palettes[MAX_PALETTES][COLORS_PER_PALETTE * VALUES_PER_COLOR] = {
+    {
+        0, 0, 0,
+        255, 0, 0,
+        0, 255, 0,
+        0, 0, 255,
+        0, 255, 255,
+        255, 0, 255,
+        255, 255, 0,
+        255, 255, 255,
+    },
+    {
+        4, 12, 6,
+        17, 35, 24,
+        30, 58, 41,
+        48, 93, 66,
+        77, 128, 97,
+        137, 162, 87,
+        190, 220, 127,
+        238, 255, 204,
+    },
+    {
+        21, 25, 26,
+        138, 76, 88,
+        217, 98, 117,
+        230, 184, 193,
+        69, 107, 115,
+        75, 151, 166,
+        165, 189, 194,
+        255, 245, 247,
+    }
+};
+
+static const char *paletteText[] = {
+    "3-BIT RGB",
+    "AMMO-8 (GameBoy-like)",
+    "RKBV (2-strip film)"
+};
+
+int main()
+{
+    // Initialization
+    //--------------------------------------------------------------------------------------
+    int screenWidth = 800;
+    int screenHeight = 450;
+
+    InitWindow(screenWidth, screenHeight, "raylib [shaders] example - palette-switch shader");
+
+    // Load shader to be used on some parts drawing
+    // NOTE 1: Using GLSL 330 shader version, on OpenGL ES 2.0 use GLSL 100 shader version
+    // NOTE 2: Defining 0 (NULL) for vertex shader forces usage of internal default vertex shader
+    Shader shader = LoadShader(0, FormatText("resources/shaders/glsl%i/palette-switch.fs", GLSL_VERSION));
+
+    // Get variable (uniform) location on the shader to connect with the program
+    // NOTE: If uniform variable could not be found in the shader, function returns -1
+    int paletteLoc = GetShaderLocation(shader, "palette");
+
+    // Initial index not set, will be automatically bounded below.
+    int currentPalette = -1;
+
+    //--------------------------------------------------------------------------------------
+
+    // Main game loop
+    while (!WindowShouldClose())            // Detect window close button or ESC key
+    {
+        // Update
+        //----------------------------------------------------------------------------------
+        int paletteIndex = currentPalette;
+        if (IsKeyPressed(KEY_RIGHT)) paletteIndex++;
+        else if (IsKeyPressed(KEY_LEFT)) paletteIndex--;
+
+        if (paletteIndex >= MAX_PALETTES) paletteIndex = 0;
+        else if (paletteIndex < 0) paletteIndex = MAX_PALETTES - 1;
+
+        // Send new value to the shader to be used on drawing.
+        // Note that we are sending RGB triplets w/o the alpha channel *only* if the current
+        // palette index has changed (in order to save performances).
+        if (currentPalette != paletteIndex) {
+            currentPalette = paletteIndex;
+            SetShaderValueArrayi(shader, paletteLoc, palettes[currentPalette], VALUES_PER_COLOR, COLORS_PER_PALETTE);
+        }
+        //----------------------------------------------------------------------------------
+
+        // Draw
+        //----------------------------------------------------------------------------------
+        BeginDrawing();
+
+            ClearBackground(RAYWHITE);
+
+            BeginShaderMode(shader);
+
+                // Draw horizontal screen-wide rectangles with increasing "palette index".
+                // The used palette index is encoded in the RGB components of the pixel.
+                int linesPerRectangle = screenHeight / COLORS_PER_PALETTE;
+                int leftover = screenHeight % COLORS_PER_PALETTE;
+                int y = 0;
+
+                for (int i = 0; i < COLORS_PER_PALETTE; ++i) {
+                    int height = linesPerRectangle;
+                    if (leftover > 0) {
+                        height += 1;
+                        leftover -= 1;
+                    }
+
+                    DrawRectangle(0, y, screenWidth, height, CLITERAL{ i, i, i, 255 });
+
+                    y += height;
+                }
+
+            EndShaderMode();
+
+            DrawText("CURRENT PALETTE:", 10, 15, 20, RAYWHITE);
+            DrawText(paletteText[currentPalette], 240, 15, 20, RED);
+            DrawText("< >", 540, 10, 30, DARKBLUE);
+
+            DrawFPS(700, 15);
+
+        EndDrawing();
+        //----------------------------------------------------------------------------------
+    }
+
+    // De-Initialization
+    //--------------------------------------------------------------------------------------
+    UnloadShader(shader);       // Unload shader
+
+    CloseWindow();                  // Close window and OpenGL context
+    //--------------------------------------------------------------------------------------
+
+    return 0;
+}