godot-shader-lab

--- name: godot-shader-lab description: | Iterative shader development with visual feedback loops via MCP tools. Edit shader code, see results via screenshots, analyze, and refine. Triggers on: shader, visual effect, material, shader code, write a shader, edit shader, shader not working, glsl, gdshader --- # Shader Lab Develop and iterate on Godot shaders with a visual feedback loop. Every edit is verified via screenshot. ## Prerequisites - Godot editor open with project loaded - godot-mcp-pro server connected - A node to apply the shader to (mesh, sprite, particle, etc.) ## Workflow ### Step 1: Classify Shader Type | User Wants | Shader Type | Template | |-----------|------------|---------| | 3D surface effect (glow, dissolve, toon) | `shader_type spatial;` | See spatial recipes | | 2D sprite/UI effect (pixelate, vignette) | `shader_type canvas_item;` | See canvas_item recipes | | Custom particle behavior | `shader_type particles;` | See particles recipes | | Sky or fog effect | `shader_type sky;` / `shader_type fog;` | See sky/fog recipes | ### Step 2: Create or Edit Shader **New shader:** 1. `mcp__godot-mcp-pro__create_shader` -- create .gdshader file with type and initial code 2. `mcp__godot-mcp-pro__assign_shader_material` -- create ShaderMaterial and assign to target node 3. `mcp__godot-mcp-pro__set_shader_param` -- set initial uniform values **Edit existing:** 1. `mcp__godot-mcp-pro__read_shader` -- read current shader code 2. `mcp__godot-mcp-pro__edit_shader` -- modify via search-replace or full replacement 3. `mcp__godot-mcp-pro__get_shader_params` -- check current parameter values ### Step 3: Visual Feedback Loop This is the core of the skill. Repeat until the visual result matches intent: ``` LOOP: 1. Edit shader code (create_shader or edit_shader) 2. Set parameters (set_shader_param) 3. Capture result: - Editor preview: mcp__godot-mcp-pro__get_editor_screenshot - Runtime preview: play_scene + get_game_screenshot + stop_scene 4. Analyze the screenshot: - Does it match the desired effect? - What's wrong? (too bright, wrong color, no effect visible, artifacts) 5. If not right: - Diagnose (see troubleshooting below) - Adjust shader code or parameters - GOTO 1 6. If satisfied: DONE ``` ### Step 4: Troubleshooting **Nothing visible:** 1. `mcp__godot-mcp-pro__get_editor_errors` -- check for shader compilation errors 2. Verify material is assigned: `mcp__godot-mcp-pro__get_node_properties` on the target node, check `material` or `material_override` 3. Check shader_type matches node type (spatial for MeshInstance3D, canvas_item for Sprite2D/Control) 4. For 3D: check the mesh has UV coordinates (primitives do, but imported meshes might not) 5. Check uniform types match set_shader_param values **Effect too subtle / too strong:** - Adjust uniform values with `mcp__godot-mcp-pro__set_shader_param` - Common: multiply effect intensity, adjust color brightness, change blend mode **Artifacts / visual errors:** - Check UV coordinates: `VERTEX.xy`, `UV`, `SCREEN_UV` usage - Check division by zero in shader math - Check texture assignments and sampler uniforms - For transparency: check `render_mode` includes appropriate flags (blend_mix, unshaded, etc.) **Performance issues:** - `mcp__godot-mcp-pro__get_performance_monitors` to check GPU impact - Reduce texture lookups, loop iterations, complex math - Use `hint_screen_texture` instead of re-reading backbuffer repeatedly ## Spatial Shader Quick Reference ```glsl shader_type spatial; // Render modes (common) render_mode unshaded; // No lighting render_mode blend_mix; // Standard alpha blending render_mode cull_disabled; // Double-sided render_mode depth_draw_opaque; // Write to depth buffer // Vertex function -- modify geometry void vertex() { VERTEX += NORMAL * displacement; // Push along normal // UV, VERTEX, NORMAL, COLOR available } // Fragment function -- modify surface appearance void fragment() { ALBEDO = vec3(1.0, 0.0, 0.0); // Surface color EMISSION = vec3(0.5); // Self-illumination ALPHA = 0.5; // Transparency ROUGHNESS = 0.8; // Surface roughness METALLIC = 0.0; // Metallic-ness // UV, SCREEN_UV, FRAGCOORD, TIME, NORMAL available } ``` ## Canvas Item Shader Quick Reference ```glsl shader_type canvas_item; void fragment() { vec4 tex = texture(TEXTURE, UV); // Sample sprite texture COLOR = tex; // Output color // UV, SCREEN_UV, TEXTURE, TIME, AT_LIGHT_PASS available } ``` ## Project Conventions Check the project's .claude/skills/ and CLAUDE.md for project-specific shader conventions such as color palettes, shader directories, performance budgets, and existing effect libraries. ## Common Patterns ### Uniform Animation via GDScript Many effects need GDScript to animate shader params: ```gdscript # Tween a shader parameter var mat: ShaderMaterial = node.material var tw: Tween = create_tween() tw.tween_method(func(v: float) -> void: mat.set_shader_parameter("amount", v) , 0.0, 1.0, duration) ``` ### Time-Based Animation in Shader ```glsl float wave = sin(TIME * speed) * 0.5 + 0.5; // 0-1 oscillation float pulse = sin(TIME * speed); // -1 to 1 ``` ## Recipe Book See `${CLAUDE_SKILL_DIR}/shader-recipes.md` for 12 complete, copy-paste-ready shader recipes with MCP tool sequences.