[wip] rlDrawMeshInstanced (#1318)

* rlDrawMeshInstanced first attempt

* rlDrawMeshInstanced OpenGL 3.3 and VAO checks

* rlDrawMeshInstanced GetShaderAttribLocation; comments

* example instanced shader

* RLGL_STANDALONE RAYMATH_STANDALONE Vector4

* apply suggested naming changes; add instanced mesh example

* remove orphan variables

6 files changed, 307 insertions, 4 deletions

diff --git a/examples/Makefile b/examples/Makefile
index 6ca8b6cf..a218cf9e 100644
--- a/examples/Makefile
+++ b/examples/Makefile
@@ -488,7 +488,8 @@ SHADERS = \
     shaders/shaders_basic_lighting \
     shaders/shaders_fog \
     shaders/shaders_simple_mask \
-    shaders/shaders_spotlight
+    shaders/shaders_spotlight \
+    shaders/shaders_rlgl_mesh_instanced
     
 AUDIO = \
     audio/audio_module_playing \
diff --git a/examples/shaders/resources/shaders/glsl330/base_lighting_instanced.vs b/examples/shaders/resources/shaders/glsl330/base_lighting_instanced.vs
new file mode 100644
index 00000000..5e5430b3
--- /dev/null
+++ b/examples/shaders/resources/shaders/glsl330/base_lighting_instanced.vs
@@ -0,0 +1,36 @@
+#version 330
+
+// Input vertex attributes
+in vec3 vertexPosition;
+in vec2 vertexTexCoord;
+in vec3 vertexNormal;
+in vec4 vertexColor;
+
+layout (location = 12) in mat4 instance;
+
+// Input uniform values
+uniform mat4 mvp;
+
+// Output vertex attributes (to fragment shader)
+out vec3 fragPosition;
+out vec2 fragTexCoord;
+out vec4 fragColor;
+out vec3 fragNormal;
+
+// NOTE: Add here your custom variables
+
+void main()
+{
+    // Send vertex attributes to fragment shader
+    fragPosition = vec3(instance * vec4(vertexPosition, 1.0));
+    fragTexCoord = vertexTexCoord;
+    fragColor = vertexColor;
+
+    mat3 normalMatrix = transpose(inverse(mat3(instance)));
+    fragNormal = normalize(normalMatrix * vertexNormal);
+
+    mat4 mvpi = mvp * instance;
+
+    // Calculate final vertex position
+    gl_Position = mvpi * vec4(vertexPosition, 1.0);
+}
diff --git a/examples/shaders/shaders_rlgl_mesh_instanced.c b/examples/shaders/shaders_rlgl_mesh_instanced.c
new file mode 100644
index 00000000..6ef421f2
--- /dev/null
+++ b/examples/shaders/shaders_rlgl_mesh_instanced.c
@@ -0,0 +1,140 @@
+/*******************************************************************************************
+*
+*   raylib [shaders] example - rlgl module usage for instanced meshes
+*
+*   This example uses [rlgl] module funtionality (pseudo-OpenGL 1.1 style coding)
+*
+*   This example has been created using raylib 3.0 (www.raylib.com)
+*   raylib is licensed under an unmodified zlib/libpng license (View raylib.h for details)
+*
+*   Copyright (c) 2018 Ramon Santamaria (@raysan5)
+*
+********************************************************************************************/
+
+#define GRAPHICS_API_OPENGL_33
+#define GLSL_VERSION 330
+
+#include <stdlib.h>
+#include "raylib.h"
+#include "raymath.h"
+#include "rlgl.h"
+
+#define RLIGHTS_IMPLEMENTATION
+#include "rlights.h"
+
+//------------------------------------------------------------------------------------
+// Program main entry point
+//------------------------------------------------------------------------------------
+int main(void)
+{
+    // Initialization
+    //--------------------------------------------------------------------------------------
+    const int screenWidth = 1024;
+    const int screenHeight = 768;
+
+    SetConfigFlags(FLAG_MSAA_4X_HINT);  // Enable Multi Sampling Anti Aliasing 4x (if available)
+    InitWindow(screenWidth, screenHeight, "raylib [shaders] example - rlgl module usage for instanced meshes");
+
+    // Define the camera to look into our 3d world
+    Camera camera = { 0 };
+    camera.position = (Vector3){ 125.0f, 125.0f, 125.0f };
+    camera.target = (Vector3){ 0.0f, 0.0f, 0.0f };
+    camera.up = (Vector3){ 0.0f, 1.0f, 0.0f };
+    camera.fovy = 45.0f;
+    camera.type = CAMERA_PERSPECTIVE;
+
+    SetCameraMode(camera, CAMERA_FREE);
+
+    const int count = 10000;                                 // Number of instances to display 
+    Mesh cube = GenMeshCube(1.0f, 1.0f, 1.0f);
+
+    Matrix* rotations = RL_MALLOC(count * sizeof(Matrix));    // Rotation state of instances
+    Matrix* rotationsInc = RL_MALLOC(count * sizeof(Matrix)); // Per-frame rotation animation of instances
+    Matrix* translations = RL_MALLOC(count * sizeof(Matrix)); // Locations of instances
+
+    // Scatter random cubes around
+    for (int i = 0; i < count; i++)
+    {
+        float x = GetRandomValue(-50, 50);
+        float y = GetRandomValue(-50, 50);
+        float z = GetRandomValue(-50, 50);
+        translations[i] = MatrixTranslate(x, y, z); 
+
+        x = GetRandomValue(0, 360);
+        y = GetRandomValue(0, 360);
+        z = GetRandomValue(0, 360);
+        Vector3 axis = Vector3Normalize((Vector3){x, y, z});
+        float angle = (float)GetRandomValue(0, 10) * DEG2RAD;
+
+        rotationsInc[i] = MatrixRotate(axis, angle);
+
+        rotations[i] = MatrixIdentity();
+    }
+
+    Matrix* transforms = RL_MALLOC(count * sizeof(Matrix));   // Pre-multiplied transformations passed to rlgl
+
+    Shader shader = LoadShader(FormatText("resources/shaders/glsl%i/base_lighting_instanced.vs", GLSL_VERSION), 
+                               FormatText("resources/shaders/glsl%i/lighting.fs", GLSL_VERSION));
+
+    // Get some shader loactions
+    shader.locs[LOC_MATRIX_MVP] = GetShaderLocation(shader, "mvp");
+    shader.locs[LOC_VECTOR_VIEW] = GetShaderLocation(shader, "viewPos");
+    shader.locs[LOC_MATRIX_MODEL] = GetShaderLocationAttrib(shader, "instance");
+
+    // ambient light level
+    int ambientLoc = GetShaderLocation(shader, "ambient");
+    SetShaderValue(shader, ambientLoc, (float[4]){ 0.2f, 0.2f, 0.2f, 1.0f }, UNIFORM_VEC4);
+
+    CreateLight(LIGHT_DIRECTIONAL, (Vector3){ 50, 50, 0 }, Vector3Zero(), WHITE, shader);
+
+    Material material = LoadMaterialDefault();
+    material.shader = shader;
+    material.maps[MAP_DIFFUSE].color = RED;
+
+    SetTargetFPS(60);                   // Set our game to run at 60 frames-per-second
+    //--------------------------------------------------------------------------------------
+
+    // Main game loop
+    while (!WindowShouldClose())        // Detect window close button or ESC key
+    {
+        // Update
+        //----------------------------------------------------------------------------------
+        UpdateCamera(&camera);
+
+        // Update the light shader with the camera view position
+        float cameraPos[3] = { camera.position.x, camera.position.y, camera.position.z };
+        SetShaderValue(shader, shader.locs[LOC_VECTOR_VIEW], cameraPos, UNIFORM_VEC3);
+
+        // Apply per-instance rotations
+        for (int i = 0; i < count; i++)
+        {
+            rotations[i] = MatrixMultiply(rotations[i], rotationsInc[i]);
+            transforms[i] = MatrixMultiply(rotations[i], translations[i]);
+        }
+
+        //----------------------------------------------------------------------------------
+
+        // Draw
+        //----------------------------------------------------------------------------------
+        BeginDrawing();
+
+            ClearBackground(RAYWHITE);
+
+            BeginMode3D(camera);
+                rlDrawMeshInstanced(cube, material, transforms, count);
+            EndMode3D();
+
+            DrawText("A CUBE OF DANCING CUBES!", 400, 10, 20, MAROON);
+            DrawFPS(10, 10);
+
+        EndDrawing();
+        //----------------------------------------------------------------------------------
+    }
+
+    // De-Initialization
+    //--------------------------------------------------------------------------------------
+    CloseWindow();        // Close window and OpenGL context
+    //--------------------------------------------------------------------------------------
+
+    return 0;
+}
diff --git a/src/raylib.h b/src/raylib.h
index 499650c6..15ff9554 100644
--- a/src/raylib.h
+++ b/src/raylib.h
@@ -1372,6 +1372,7 @@ RLAPI void SetShapesTexture(Texture2D texture, Rectangle source);         // Def
 
 // Shader configuration functions
 RLAPI int GetShaderLocation(Shader shader, const char *uniformName);      // Get shader uniform location
+RLAPI int GetShaderLocationAttrib(Shader shader, const char *attribName); // Get shader attribute location
 RLAPI void SetShaderValue(Shader shader, int uniformLoc, const void *value, int uniformType);               // Set shader uniform value
 RLAPI void SetShaderValueV(Shader shader, int uniformLoc, const void *value, int uniformType, int count);   // Set shader uniform value vector
 RLAPI void SetShaderValueMatrix(Shader shader, int uniformLoc, Matrix mat);         // Set shader uniform value (matrix 4x4)
diff --git a/src/raymath.h b/src/raymath.h
index 3e5e1973..783c4449 100644
--- a/src/raymath.h
+++ b/src/raymath.h
@@ -114,13 +114,16 @@
         float z;
     } Vector3;
 
-    // Quaternion type
-    typedef struct Quaternion {
+    // Vector4 type
+    typedef struct Vector4 {
         float x;
         float y;
         float z;
         float w;
-    } Quaternion;
+    } Vector4;
+
+    // Quaternion type
+    typedef Vector4 Quaternion;
 
     // Matrix type (OpenGL style 4x4 - right handed, column major)
     typedef struct Matrix {
diff --git a/src/rlgl.h b/src/rlgl.h
index 0869d118..44bcf381 100644
--- a/src/rlgl.h
+++ b/src/rlgl.h
@@ -560,6 +560,7 @@ RLAPI void rlLoadMesh(Mesh *mesh, bool dynamic);                          // Upl
 RLAPI void rlUpdateMesh(Mesh mesh, int buffer, int count);                // Update vertex or index data on GPU (upload new data to one buffer)
 RLAPI void rlUpdateMeshAt(Mesh mesh, int buffer, int count, int index);   // Update vertex or index data on GPU, at index
 RLAPI void rlDrawMesh(Mesh mesh, Material material, Matrix transform);    // Draw a 3d mesh with material and transform
+RLAPI void rlDrawMeshInstanced(Mesh mesh, Material material, Matrix *transforms, int count);    // Draw a 3d mesh with material and transform
 RLAPI void rlUnloadMesh(Mesh mesh);                                       // Unload mesh data from CPU and GPU
 
 // NOTE: There is a set of shader related functions that are available to end user,
@@ -582,6 +583,7 @@ RLAPI Rectangle GetShapesTextureRec(void);                                // Get
 
 // Shader configuration functions
 RLAPI int GetShaderLocation(Shader shader, const char *uniformName);              // Get shader uniform location
+RLAPI int GetShaderLocationAttrib(Shader shader, const char *attribName);         // Get shader attribute location
 RLAPI void SetShaderValue(Shader shader, int uniformLoc, const void *value, int uniformType);               // Set shader uniform value
 RLAPI void SetShaderValueV(Shader shader, int uniformLoc, const void *value, int uniformType, int count);   // Set shader uniform value vector
 RLAPI void SetShaderValueMatrix(Shader shader, int uniformLoc, Matrix mat);       // Set shader uniform value (matrix 4x4)
@@ -2860,6 +2862,113 @@ void rlDrawMesh(Mesh mesh, Material material, Matrix transform)
 #endif
 }
 
+// Draw a 3d mesh with material and transform
+void rlDrawMeshInstanced(Mesh mesh, Material material, Matrix *transforms, int count)
+{
+#if defined(GRAPHICS_API_OPENGL_33)
+
+    if (!RLGL.ExtSupported.vao) {
+        TRACELOG(LOG_ERROR, "VAO: Instanced rendering requires VAO support");
+        return;
+    }
+
+    // Bind shader program
+    glUseProgram(material.shader.id);
+
+    // Upload to shader material.colDiffuse
+    if (material.shader.locs[LOC_COLOR_DIFFUSE] != -1)
+        glUniform4f(material.shader.locs[LOC_COLOR_DIFFUSE], (float)material.maps[MAP_DIFFUSE].color.r/255.0f,
+                                                           (float)material.maps[MAP_DIFFUSE].color.g/255.0f,
+                                                           (float)material.maps[MAP_DIFFUSE].color.b/255.0f,
+                                                           (float)material.maps[MAP_DIFFUSE].color.a/255.0f);
+
+    // Upload to shader material.colSpecular (if available)
+    if (material.shader.locs[LOC_COLOR_SPECULAR] != -1)
+        glUniform4f(material.shader.locs[LOC_COLOR_SPECULAR], (float)material.maps[MAP_SPECULAR].color.r/255.0f,
+                                                               (float)material.maps[MAP_SPECULAR].color.g/255.0f,
+                                                               (float)material.maps[MAP_SPECULAR].color.b/255.0f,
+                                                               (float)material.maps[MAP_SPECULAR].color.a/255.0f);
+
+    // Bind active texture maps (if available)
+    for (int i = 0; i < MAX_MATERIAL_MAPS; i++)
+    {
+        if (material.maps[i].texture.id > 0)
+        {
+            glActiveTexture(GL_TEXTURE0 + i);
+            if ((i == MAP_IRRADIANCE) || (i == MAP_PREFILTER) || (i == MAP_CUBEMAP))
+                glBindTexture(GL_TEXTURE_CUBE_MAP, material.maps[i].texture.id);
+            else glBindTexture(GL_TEXTURE_2D, material.maps[i].texture.id);
+
+            glUniform1i(material.shader.locs[LOC_MAP_DIFFUSE + i], i);
+        }
+    }
+
+    // Bind vertex array objects (or VBOs)
+    glBindVertexArray(mesh.vaoId);
+
+    // At this point the modelview matrix just contains the view matrix (camera)
+    // For instanced shaders "mvp" is not premultiplied by any instance transform, only RLGL.State.transform
+    glUniformMatrix4fv(material.shader.locs[LOC_MATRIX_MVP], 1, false, MatrixToFloat(
+        MatrixMultiply(MatrixMultiply(RLGL.State.transform, RLGL.State.modelview), RLGL.State.projection)
+    ));
+
+    float16* instances = RL_MALLOC(count * sizeof(float16));
+
+    for (int i = 0; i < count; i++)
+        instances[i] = MatrixToFloatV(transforms[i]);
+
+    // This could alternatively use a static VBO and either glMapBuffer or glBufferSubData.
+    // It isn't clear which would be reliably faster in all cases and on all platforms, and
+    // anecdotally glMapBuffer seems very slow (syncs) while glBufferSubData seems no faster
+    // since we're transferring all the transform matrices anyway.
+    unsigned int instancesB;
+    glGenBuffers(1, &instancesB);
+    glBindBuffer(GL_ARRAY_BUFFER, instancesB);
+    glBufferData(GL_ARRAY_BUFFER, count * sizeof(float16), instances, GL_STATIC_DRAW);
+
+    // Instances are put in LOC_MATRIX_MODEL attribute location with space for 4x Vector4, eg:
+    // layout (location = 12) in mat4 instance;
+    unsigned int instanceA = material.shader.locs[LOC_MATRIX_MODEL];
+
+    for (unsigned int i = 0; i < 4; i++)
+    {
+        glEnableVertexAttribArray(instanceA+i);
+        glVertexAttribPointer(instanceA+i, 4, GL_FLOAT, GL_FALSE, sizeof(Matrix), (void*)(i * sizeof(Vector4)));
+        glVertexAttribDivisor(instanceA+i, 1);
+    }
+
+    glBindBuffer(GL_ARRAY_BUFFER, 0);
+
+    // Draw call!
+    if (mesh.indices != NULL) {
+        // Indexed vertices draw
+        glDrawElementsInstanced(GL_TRIANGLES, mesh.triangleCount*3, GL_UNSIGNED_SHORT, 0, count);
+    } else {
+        glDrawArraysInstanced(GL_TRIANGLES, 0, mesh.vertexCount, count);
+    }
+
+    glDeleteBuffers(1, &instancesB);
+    RL_FREE(instances);
+
+    // Unbind all binded texture maps
+    for (int i = 0; i < MAX_MATERIAL_MAPS; i++)
+    {
+        glActiveTexture(GL_TEXTURE0 + i);       // Set shader active texture
+        if ((i == MAP_IRRADIANCE) || (i == MAP_PREFILTER) || (i == MAP_CUBEMAP)) glBindTexture(GL_TEXTURE_CUBE_MAP, 0);
+        else glBindTexture(GL_TEXTURE_2D, 0);   // Unbind current active texture
+    }
+
+    // Unind vertex array objects (or VBOs)
+    glBindVertexArray(0);
+
+    // Unbind shader program
+    glUseProgram(0);
+
+#else
+    TRACELOG(LOG_ERROR, "VAO: Instanced rendering requires GRAPHICS_API_OPENGL_33");
+#endif
+}
+
 // Unload mesh data from CPU and GPU
 void rlUnloadMesh(Mesh mesh)
 {
@@ -3183,6 +3292,19 @@ int GetShaderLocation(Shader shader, const char *uniformName)
     return location;
 }
 
+// Get shader attribute location
+int GetShaderLocationAttrib(Shader shader, const char *attribName)
+{
+    int location = -1;
+#if defined(GRAPHICS_API_OPENGL_33) || defined(GRAPHICS_API_OPENGL_ES2)
+    location = glGetAttribLocation(shader.id, attribName);
+
+    if (location == -1) TRACELOG(LOG_WARNING, "SHADER: [ID %i] Failed to find shader attribute: %s", shader.id, attribName);
+    else TRACELOG(LOG_INFO, "SHADER: [ID %i] Shader attribute (%s) set at location: %i", shader.id, attribName, location);
+#endif
+    return location;
+}
+
 // Set shader uniform value
 void SetShaderValue(Shader shader, int uniformLoc, const void *value, int uniformType)
 {