[examples] Add `core_delta_time` (#5216)

* delta example

* clarification

* made it more clear what delta time is

* more explanation

* vector2 positions, removed all warnings

* removed keys, moved global to local, conventions & comments, show target fps

* new png

* remove more periods

* another period

* remove note about conventions, remove period

examples/core/core_delta_time.c

@@ -0,0 +1,131 @@
+/*******************************************************************************************
+*
+*   raylib [core] example - delta time
+*
+*   Example complexity rating: [★☆☆☆] 1/4
+*
+*   Example originally created with raylib 5.5
+*
+*   Example contributed by Robin (@RobinsAviary) and reviewed by Ramon Santamaria (@raysan5)
+*
+*   Example licensed under an unmodified zlib/libpng license, which is an OSI-certified,
+*   BSD-like license that allows static linking with closed source software
+*
+*   Copyright (c) 2025-2025 Robin (@RobinsAviary)
+*
+********************************************************************************************/
+
+#include "raylib.h"
+
+//------------------------------------------------------------------------------------
+// Program main entry point
+//------------------------------------------------------------------------------------
+int main(void)
+{
+    // Initialization
+    //--------------------------------------------------------------------------------------
+    const int screenWidth = 800;
+    const int screenHeight = 450;
+
+    InitWindow(screenWidth, screenHeight, "raylib [core] example - delta time");
+
+    int currentFps = 60;
+
+    // Store the position for the both of the circles
+    Vector2 deltaCircle = {0, screenHeight / 3.0f};
+    Vector2 frameCircle = {0, screenHeight * (2.0f/3.0f)};
+
+    // The speed applied to both circles
+    const float speed = 10.0;
+    const float circleRadius = 32;
+
+    SetTargetFPS(currentFps);
+    //--------------------------------------------------------------------------------------
+
+    // Main game loop
+    while (!WindowShouldClose()) // Detect window close button or ESC key
+    {
+        // Update
+        //----------------------------------------------
+        if (IsKeyPressed(KEY_R)) // Reset both circles' positions when you press R
+        {
+            deltaCircle.x = 0;
+            frameCircle.x = 0;
+        }
+
+        // Adjust the FPS target based on the mouse wheel
+        float mouseWheel = GetMouseWheelMove();
+        if (mouseWheel != 0)
+        {
+            currentFps += (int)mouseWheel;
+            SetTargetFPS(currentFps);
+        }
+
+        // GetFrameTime() returns the time it took to draw the last frame, in seconds (usually called delta time)
+        // Uses the delta time to make the circle look like it's moving at a "consistent" speed regardless of FPS
+
+        // Multiply by 6.0 (an arbitrary value) in order to make the speed visually closer to the other circle (at 60 fps), for comparison
+        deltaCircle.x += GetFrameTime() * 6.0f * speed;
+        // This circle can move faster or slower visually depending on the FPS
+        frameCircle.x += .1f * speed;
+
+        // If either circle is off the screen, reset it back to the start
+        if (deltaCircle.x > screenWidth)
+        {
+            deltaCircle.x = 0;
+        }
+
+        if (frameCircle.x > screenWidth)
+        {
+            frameCircle.x = 0;
+        }
+
+        // Draw
+        //----------------------------------------------------------------------------------
+        BeginDrawing();
+
+        ClearBackground(RAYWHITE);
+
+        // Draw both circles to the screen
+        DrawCircleV(deltaCircle, circleRadius, RED);
+        DrawCircleV(frameCircle, circleRadius, BLUE);
+
+        // Determine what help text to show depending on the current FPS target
+        const char* fpsText;
+
+        if (currentFps <= 0)
+        {
+            if (currentFps < 0)
+            {
+                // Clamp values below 0
+                currentFps = 0;
+            }
+
+            // Special text for when the FPS target is set to 0 or less, which makes it unlimited
+            fpsText = TextFormat("fps: unlimited (%i)", GetFPS());
+        }
+        else
+        {
+            fpsText = TextFormat("fps: %i (target: %i)", GetFPS(), currentFps);
+        }
+
+        // Draw the help text
+        DrawText(fpsText, 10, 10, 20, DARKGRAY);
+        DrawText(TextFormat("frame time: %02.02f ms", GetFrameTime()), 10, 30, 20, DARKGRAY);
+        DrawText("use the scroll wheel to change the fps limit, r to reset", 10, 50, 20, DARKGRAY);
+
+        // Draw the text above the circles
+        DrawText("x += GetFrameTime() * speed", 10, 90, 20, RED);
+        DrawText("x += speed", 10, 240, 20, BLUE);
+
+        EndDrawing();
+        //----------------------------------------------------------------------------------
+    }
+
+    // De-Initialization
+    //--------------------------------------------------------------------------------------
+    CloseWindow();        // Close window and OpenGL context
+    //--------------------------------------------------------------------------------------
+
+    return 0;
+}