added 2d camera mouse zoom example (#129)

* added 2d camera mouse zoom example

* correctly formatted build.zig

* removed "gl" const

build.zig

@@ -220,7 +220,13 @@ pub fn build(b: *std.Build) !void {
             .name = "3d_camera_first_person",
             .path = "examples/core/3d_camera_first_person.zig",
             .desc = "Simple first person demo",
+        },        
+        .{
+            .name = "2d_camera_mouse_zoom",
+            .path = "examples/core/2d_camera_mouse_zoom.zig",
+            .desc = "Shows mouse zoom demo",
         },
+
         .{
             .name = "window_flags",
             .path = "examples/core/window_flags.zig",

examples/core/2d_camera_mouse_zoom.zig

@@ -0,0 +1,118 @@
+// port of raylib example https://github.com/raysan5/raylib/blob/master/examples/core/core_2d_camera_mouse_zoom.c
+
+const rl = @import("raylib");
+
+pub fn main() anyerror!void {
+    // Initialization
+    //--------------------------------------------------------------------------------------
+    const screenWidth = 800;
+    const screenHeight = 450;
+
+    rl.initWindow(screenWidth, screenHeight, "raylib-zig [core] example - 2d camera mouse zoom");
+    defer rl.closeWindow(); // Close window and OpenGL context
+
+    var camera = rl.Camera2D{
+        .target = .{ .x = 0, .y = 0 },
+        .offset = .{ .x = 0, .y = 0 },
+        .zoom = 1.0,
+        .rotation = 0,
+    };
+
+    var zoomMode: i32 = 0; // 0-Mouse Wheel, 1-Mouse Move
+
+    rl.setTargetFPS(60); // Set our game to run at 60 frames-per-second
+    //--------------------------------------------------------------------------------------
+
+    // Main game loop
+    while (!rl.windowShouldClose()) { // Detect window close button or ESC key
+        // Update
+        //----------------------------------------------------------------------------------
+        if (rl.isKeyPressed(.key_one)) {
+            zoomMode = 0;
+        } else if (rl.isKeyPressed(.key_two)) {
+            zoomMode = 1;
+        }
+
+        // Translate based on mouse right click
+        if (rl.isMouseButtonDown(.mouse_button_right)) {
+            var delta = rl.getMouseDelta();
+            delta = rl.math.vector2Scale(delta, -1.0 / camera.zoom);
+            camera.target = rl.math.vector2Add(camera.target, delta);
+        }
+
+        if (zoomMode == 0) {
+            // Zoom based on mouse wheel
+            const wheel = rl.getMouseWheelMove();
+            if (wheel != 0) {
+                // Get the world point that is under the mouse
+                const mouseWorldPos = rl.getScreenToWorld2D(rl.getMousePosition(), camera);
+
+                // Set the offset to where the mouse is
+                camera.offset = rl.getMousePosition();
+
+                // Set the target to match, so that the camera maps the world space point
+                // under the cursor to the screen space point under the cursor at any zoom
+                camera.target = mouseWorldPos;
+
+                // Zoom increment
+                var scaleFactor = 1.0 + (0.25 * @abs(wheel));
+                if (wheel < 0) {
+                    scaleFactor = 1.0 / scaleFactor;
+                }
+                camera.zoom = rl.math.clamp(camera.zoom * scaleFactor, 0.125, 64.0);
+            }
+        } else {
+            // Zoom based on left click
+            if (rl.isMouseButtonPressed(.mouse_button_left)) {
+                // Get the world point that is under the mouse
+                const mouseWorldPos = rl.getScreenToWorld2D(rl.getMousePosition(), camera);
+
+                // Set the offset to where the mouse is
+                camera.offset = rl.getMousePosition();
+
+                // Set the target to match, so that the camera maps the world space point
+                // under the cursor to the screen space point under the cursor at any zoom
+                camera.target = mouseWorldPos;
+            }
+            if (rl.isMouseButtonDown(.mouse_button_left)) {
+                // Zoom increment
+                const deltaX = rl.getMouseDelta().x;
+                var scaleFactor = 1.0 + (0.01 * @abs(deltaX));
+                if (deltaX < 0) {
+                    scaleFactor = 1.0 / scaleFactor;
+                }
+                camera.zoom = rl.math.clamp(camera.zoom * scaleFactor, 0.125, 64.0);
+            }
+        }
+        //----------------------------------------------------------------------------------
+
+        // Draw
+        //----------------------------------------------------------------------------------
+        rl.beginDrawing();
+        defer rl.endDrawing();
+
+        rl.clearBackground(rl.Color.ray_white);
+
+        {
+            camera.begin();
+            defer camera.end();
+
+            rl.gl.rlPushMatrix();
+            rl.gl.rlTranslatef(0, 25 * 50, 0);
+            rl.gl.rlRotatef(90, 1, 0, 0);
+            rl.drawGrid(100, 50);
+            rl.gl.rlPopMatrix();
+
+            rl.drawCircle(screenWidth / 2, screenHeight / 2, 50, rl.Color.maroon);
+        }
+
+        rl.drawText("[1][2] Select mouse zoom mode (Wheel or Move)", 20, 20, 20, rl.Color.dark_gray);
+        if (zoomMode == 0) {
+            rl.drawText("Mouse right button drag to move, mouse wheel to zoom", 20, 50, 20, rl.Color.dark_gray);
+        } else {
+            rl.drawText("Mouse right button drag to move, mouse press and move to zoom", 20, 50, 20, rl.Color.dark_gray);
+        }
+
+        //----------------------------------------------------------------------------------
+    }
+}