Add DrawTexturedPoly and example (#1677)

* adds DrawTexturedPoly with example

* the actual example ... ahem

* moved DrawTexturePoly to textures function and example
NB function name changed to fit with other DrawTextureXXX functions
(no "d" )

Co-authored-by: codifies <you@example.com>

examples/textures/textures_poly.c

@@ -0,0 +1,95 @@
+/*******************************************************************************************
+*
+*   raylib [shapes] example - Draw Textured Polygon
+*
+*   This example has been created using raylib 99.98 (www.raylib.com)
+*   raylib is licensed under an unmodified zlib/libpng license (View raylib.h for details)
+*
+*   Copyright (c) 2014 Ramon Santamaria (@raysan5)
+*   Copyright (c) 2021 Chris Camacho (codifies - bedroomcoders.co.uk)
+*
+********************************************************************************************/
+
+#include "raylib.h"
+#include "raymath.h"
+
+int main(void)
+{
+    // Initialization
+    //--------------------------------------------------------------------------------------
+    const int screenWidth = 800;
+    const int screenHeight = 450;
+
+    int numPnts = 11;  // 10 points and back to the start
+
+    Vector2 tPnts[] = {
+        (Vector2){.75,  0},
+        (Vector2){.25,  0},
+        (Vector2){0,    .5},
+        (Vector2){0,    .75},
+        (Vector2){.25,  1},
+        (Vector2){.375, .875},
+        (Vector2){.625, .875},
+        (Vector2){.75,  1},
+        (Vector2){1,    .75},
+        (Vector2){1,    .5},
+        (Vector2){.75,  0}  // close the poly
+    };
+
+    Vector2 pnts[numPnts];
+
+    // create the poly coords from the UV's
+    // you don't have to do this you can specify
+    // them however you want
+    for (int i=0; i < numPnts; i++)
+    {
+        pnts[i].x = (tPnts[i].x - 0.5) * 256.0;
+        pnts[i].y = (tPnts[i].y - 0.5) * 256.0;
+    }
+
+    InitWindow(screenWidth, screenHeight, "raylib [textures] example - Textured Polygon");
+
+    Texture tex = LoadTexture("resources/cat.png");
+
+    SetTargetFPS(60);               // Set our game to run at 60 frames-per-second
+    //--------------------------------------------------------------------------------------
+    float ang = 0;
+    // Main game loop
+    while (!WindowShouldClose())    // Detect window close button or ESC key
+    {
+        // Update
+        //----------------------------------------------------------------------------------
+        // Update your variables here
+        //----------------------------------------------------------------------------------
+        ang++;
+        
+        Vector2 dPnts[numPnts];
+        for (int i = 0; i < numPnts; i++)
+        {
+            dPnts[i] = Vector2Rotate(pnts[i], ang);
+        }
+
+        // Draw
+        //----------------------------------------------------------------------------------
+        BeginDrawing();
+
+            ClearBackground(RAYWHITE);
+
+            DrawText("Textured Polygon", 20, 20, 20, DARKGRAY);
+            
+            DrawTexturePoly(tex, screenWidth/2, screenHeight/2,
+                                dPnts, tPnts, numPnts, WHITE);
+
+        EndDrawing();
+        //----------------------------------------------------------------------------------
+    }
+    
+    UnloadTexture(tex);
+
+    // De-Initialization
+    //--------------------------------------------------------------------------------------
+    CloseWindow();        // Close window and OpenGL context
+    //--------------------------------------------------------------------------------------
+
+    return 0;
+}