[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

2 files changed, 176 insertions, 0 deletions

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;
+}