t1k:unity:dots-rendering:perspective-isometric

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Field	Value
Module	dots-rendering
Version	2.1.7
Effort	high
Tools	—

Keywords: 2.5D, DOTS, isometric, perspective

How to invoke

/t1k:unity:dots-rendering:perspective-isometric

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DOTS Perspective: Isometric

When This Skill Triggers

• Isometric, dimetric, 3/4 view, billboard sprite, BillboardSprite shader
• Perspective camera with tilt angle, billboard quad rendering
• DOTS instancing, _Cutoff instanced property

Key Concepts

• Simulation: XZ plane (always). Navigation, physics, AI on XZ
• Presentation: Perspective camera tilted ~30 degrees. Sprites on billboard quads that always face camera
• No coordinate remapping — camera angle provides the isometric look naturally

Camera Setup

• Perspective (not orthographic) with ~60 degree FOV
• Position: (0, height, -backOffset), rotation: (TiltAngle, 0, 0)
• Auto-zoom: adjust distance based on battle AABB extents and FOV
• Smooth lerp position and distance -> See references/isometric-camera-guide.md

Rendering

• BillboardSprite.shader — custom HLSL shader in dots-rpg/Runtime/Rendering/
• 3 URP passes: Forward, ShadowCaster, DepthOnly
• Billboard vertex transform: offset from object center along camera right/up vectors
• _Cutoff is DOTS-instanced for per-entity alpha clip control
• Cutout rendering (AlphaTest queue) for SRP Batcher compatibility -> See references/isometric-rendering-guide.md

Navigation

• Standard XZ NavMeshSurface on visible ground plane
• NavigationAuthoring.EnableGrounding = false (flat billboard quads, no Y physics)
• Obstacles are visible 3D cubes with URP/Lit materials (unlike 2D where they are invisible)
• NavMeshObstacle.carving = true + (StaticEditorFlags)8 + area 1 (Not Walkable)

Animation

• SpriteAnimationAuthoring for sprite sheet UV animation (same as 2D)
• Front-facing character silhouette sprites (not side-profile like side-view)
• Billboard shader handles camera-facing orientation automatically
• Direction-aware sprites possible via multiple sprite sheets + facing direction

Billboard Vertex Transform (Key Pattern)

// Object center in world space
float3 centerWS = TransformObjectToWorld(float3(0, 0, 0));

// Extract per-axis scale from object-to-world matrix
float3 scaleX = float3(UNITY_MATRIX_M[0][0], UNITY_MATRIX_M[1][0], UNITY_MATRIX_M[2][0]);
float3 scaleY = float3(UNITY_MATRIX_M[0][1], UNITY_MATRIX_M[1][1], UNITY_MATRIX_M[2][1]);

// Camera right and up vectors
float3 camRight = normalize(UNITY_MATRIX_V[0].xyz);
float3 camUp    = normalize(UNITY_MATRIX_V[1].xyz);

// Billboard: offset from center along camera-plane axes
float3 worldPos = centerWS
    + camRight * input.positionOS.x * length(scaleX)
    + camUp    * input.positionOS.y * length(scaleY);

DOTS Instancing Setup

#ifdef DOTS_INSTANCING_ON
    UNITY_DOTS_INSTANCING_START(MaterialPropertyMetadata)
        UNITY_DOTS_INSTANCED_PROP(float4, _BaseMap_ST)
        UNITY_DOTS_INSTANCED_PROP(float4, _BaseColor)
        UNITY_DOTS_INSTANCED_PROP(float , _Cutoff)
    UNITY_DOTS_INSTANCING_END(MaterialPropertyMetadata)
#endif

Gotchas

#	Issue	Fix
1	Billboard shader needs #pragma target 4.5 for DOTS instancing	Without it, UNITY_DOTS_INSTANCED_PROP macros fail silently
2	Shadow acne on billboard quads	Use ApplyShadowBias() in ShadowCaster pass with billboard normal
3	Billboard normal for shadows = -normalize(UNITY_MATRIX_V[2].xyz)	Camera forward as approximate face normal
4	Cull Off required on all passes	Billboard quads can face either direction relative to light
5	Ground material uses URP/Lit (not Unlit)	Iso view shows ground surface, needs lighting

Cross-References

• dots-ecs — ECS fundamentals
• dots-rpg — BillboardSprite.shader, SpriteAnimation components
• dots-graphics — DOTS instancing, MaterialProperty overrides
• dots-shader — Custom HLSL shader authoring agent
• unity-urp — URP shader library, render passes
• agents-navigation — XZ pathfinding

Reference Files

File	Coverage
references/isometric-rendering-guide.md	Billboard shader, DOTS instancing, cutout materials, shadow pass
references/isometric-camera-guide.md	Perspective iso camera, auto-zoom, tilt math, FOV-based framing