Game Programming 08 OGRE3D Material in Action

1. Game Programming 08OGRE3D Material in Action 2010년 2학기 디지털콘텐츠전공

2. Rendering in Video Games • Depth-Buffered Triangle Rasterization • Virtual Scene • Virtual Camera • Various Light Sources • Visual Properties • Solving the Rendering Equation (Shading Equation)

3. Rendering in OGRE3D • Depth-Buffered Triangle Rasterization • Virtual Scene  createScene() • Virtual Camera  createCamera()/ createViewport() • Various Light Sources  createScene() • Visual Properties  material • Solving the Rendering Equation (OGRE3D engine)

4. Materials in general • The Material controls how objects look in the scene • Basic surface properties such as: • reflectance, diffuse color, shininess, etc. • How to use textures • What images to be used • How many and how to blend them • Special effects such as: • Environmental mapping • Culling mode • filtering

5. Materials in OGRE • SceneManager class manages the list of materials available to the scene • To ways of loading a material • Creating and tweaking it by a code • MaterialManager • Using a script to be loaded at runtime • Material Script

6. Material Script • OGRE Material Script: • File name: ‘’*.material ’’ • A text file which describe a material • Easy to define a complex material • Reuse easily for different games • How to load • OGRE looks for *.material files in all resource locations. • Call ‘load’ method in order to complete the loading process otherwise, the materials are not available.

7. Material Script: Format // This is a comment material walls/funkywall1 { // first, preferred technique technique { // first pass pass { ambient 0.5 0.5 0.5 diffuse 1.0 1.0 1.0 // Texture unit 0 texture_unit { texture wibbly.jpg scroll_anim 0.1 0.0 wave_xform scale sine 0.0 0.7 0.0 1.0 } // Texture unit 1 (this is a multitexture pass) texture_unit { texture wobbly.png rotate_anim 0.25 colour_op add } } } }

8. Material Script: Name • Material name • Should be unique • ‘/’ is used for grouping conceptually • ‘:’ can be used after the name for inherit from other existing material // This is a comment material walls/funkywall1 { …… }

9. Material Script: Technique // This is a comment material walls/funkywall1 { // first, preferred technique technique { ……… } // second, preferred technique technique { ……… } } • Technique • Define how the material looks • Can have multiple techniques used as a fallback or in a different LOD level. • Each Technique is made up of multiple passes

10. Material Script: Pass • Single Pass • One single rendering with a given setup • A pass has global attributes such as ambient, diffuse, etc. • A pass can have a texture unit or multiple texture units • Multiple Passes (1~16 passes) • Rendering can be done multiple times with different setup • The final rendering result will be obtained by compositing every results from the passes. material walls/funkywall1 { technique { // first pass pass { …… } } }

11. Material Script: Pass • Global attributes • Ambient color • Format: ambient (<red> <green> <blue> [<alpha>]| vertexcolour) • Example: ambient 0.0 0.8 0.0 • Default: ambient 1.0 1.0 1.0 1.0 • Diffuse color • Format: diffuse (<red> <green> <blue> [<alpha>]| vertexcolour) • Example: diffuse 1.0 0.5 0.5 • Default: diffuse 1.0 1.0 1.0 1.0 • Specular color • Format: specular (<red> <green> <blue> [<alpha>]| vertexcolour) <shininess> • Example: specular 1.0 1.0 1.0 12.5 • Shininess: any value between 0~128 (the bigger, the sharper) • Default: specular 0.0 0.0 0.0 0.0 0.0

12. Material Script: Pass • Global attributes • scene_blend • How to blend the pass with the existing scene content • Flexible version: • Format: scene_blend <src_factor> <dest_factor> • Meaning: (pass_result * sourceFactor) + (scene_pixel * destFactor) • Factors: one | zero | src_color | one_minus_src_colour | dest_colour | one_minus_dest_colour | dest_alpha | one_minus_dest_alpha | src_alpha | one_minus_src_alpha • Example: scene_blend one one_minus_dest_alpha • Simpler version • Format2: scene_blend <add | modulate | alpha_blend | colour_blend> • Meaning: • add: 'scene_blend one one‘ (explosions, flares, lights, ghosts) • modulate: 'scene_blend dest_colour zero‘ (darkening, smoked glass) • colour_blend: 'scene_blend src_colour one_minus_src_colour' • alpha_blend: 'scene_blend src_alpha one_minus_src_alpha‘ • Example: scene_blend add • scene_blend_op • Specify the operation in scene blending • Format: scene_blend_op <add | subtract | reverse_subtract | min | max> • Meaning: (pass_result * sourceFactor) +(-) (scene_pixel * destFactor) • Default: scene_blend_op add

13. Material Script: Pass • Global attributes • Lighting on/off • Format: lighting <on | off> • If off, all objects will be fully lit. • Default: lighting on • Shading • Format: shading <flat | gouraud | phong> • Default: shading gouraud • Polygon mode • Format: polygon_mode <solid | wireframe | points> • Default: polygon_mode solid

14. Material Script: Pass • Global attributes • Depth check • Format: depth_check <on|off> • Default: depth_check on • Depth write • Format: depth_write <on|off> • Default: depth_write on • Depth function • Determine how to check the depth • Format: depth_func <func> • <func> • always_fail : Never writes a pixel to the render target • always_pass : Always writes a pixel to the render target • less : Write if (new_Z < existing_Z) • less_equal : Write if (new_Z <= existing_Z) • equal : Write if (new_Z == existing_Z) • not_equal : Write if (new_Z != existing_Z) • greater_equal : Write if (new_Z >= existing_Z) • greater :Write if (new_Z >existing_Z) • Default: depth_func less_equal

15. Material Script: texture_unit • Texture • Set name of the texture image • Format: texture <texturename> [<type>] [unlimited | numMipMaps] [alpha] [<PixelFormat>] [gamma] • Example: texture funkywall.jpg • Animated texture • Set the images to be used in animated texture • Format1 (short): anim_texture <base_name> <num_frames> <duration> • Example: anim_texture flame.jpg 3 1.5 • Meaning: load 3 frames (frame_0.jpg, frame_1.jpg, frame_2.jpg) for 1.5 sec. • Format2 (long): anim_texture <frame1> <frame2> ... <duration> • Example: anim_texture flamestart.jpg flamemore.png flameagain.jpg 1.5

16. Material Script: texture_unit • Texture coordinate set • Sets which texture coordinate set is to be used • Format: tex_coord_set <set_num> • Example: tex_coord_set 2 • Texture address mode • Defines what happens when uv values exceed 1.0 • Simple Format: tex_address_mode <uv_mode> • Extended Format: tex_address_mode <u_mode> <v_mode> • Mode: <wrap | clamp | mirror | border> • Texture border color • Set the border color when thexture address mode is border • Format: tex_border_colour <red> <green> <blue> [<alpha>] • Example: tex_border_colour 0.0 1.0 0.3

17. Material Script: texture_unit • Color operation • Determines how the color of this texture layer is combined with the one below it • Format: colour_op <operation_type> • Operation types: • replace : Replace all color with texture with no adjustment • add : Add color components together. • modulate : Multiply colour components together • alpha_blend : Blend based on texture alpha • Default: colour_op modulate

18. Material Script: texture_unit • Texture Transformation • Scroll • Sets a fixed scroll offset for the texture. • Format: scroll <x> <y> • Scrolling animation • Sets up an animated scroll for the texture layer • Format: scroll_anim <xspeed> <yspeed> • Rotate • Format: rotate <angle> • Rotating animation • Format: rotate_anim <revs_per_second> • Scale • Format: scale <x_scale> <y_scale>

19. Material Script: texture_unit • Advanced Texture Transformation • Animation using wave function • Format: wave_xform <xform_type> <wave_type> <base> <frequency> <phase> <amplitude> • Example: wave_xform scale_x sine 1.0 0.2 0.0 5.0 • xform_types: • scroll_x : Animate the x scroll value • scroll_y : Animate the y scroll value • rotate : Animate the rotate value • scale_x : Animate the x scale value • scale_y : Animate the y scale value • wave_types: • sine • A typical sine wave which smoothly loops between min and max values • triangle • An angled wave which increases & decreases at constant speed, changing instantly at the extremes • square • Max for half the wavelength, min for the rest with instant transition between • sawtooth • Gradual steady increase from min to max over the period with an instant return to min at the end. • inverse_sawtooth • Gradual steady decrease from max to min over the period, with an instant return to max at the end. • Base: The base value, the minimum if amplitude > 0, the maximum if amplitude < 0

20. Material Script: other functions • There are other advanced shader-based functions in Material script • Vertex/geometry/fragment programs • CG programs • HLSL programs • GLSL programs

21. Reference for the materials • http://www.ogre3d.org/tikiwiki/Materials

22. Manual Creation • Using MaterialManager Ogre::MaterialPtr material = Ogre::MaterialManager::getSingleton().create ( "Test/ColourTest", Ogre::ResourceGroupManager::DEFAULT_RESOURCE_GROUP_NAME ); material->getTechnique(0)->getPass(0)->setDiffuse(Ogre::ColourValue(1.0,0.0,0.0));

23. Material basic attributes • ambient reflectance = ColourValue::White (full) • diffuse reflectance = ColourValue::White (full) • specular reflectance = ColourValue::Black (none) • emmissive = ColourValue::Black (none) • shininess = 0 (not shiny) • No texture layers (& hence no textures) • SourceBlendFactor = SBF_ONE, DestBlendFactor = SBF_ZERO (opaque) • Depth buffer checking = on • Depth buffer writing = on • Depth buffer comparison function = CMPF_LESS_EQUAL • Culling mode = CULL_CLOCKWISE • Ambient lighting in scene = ColourValue(0.5, 0.5, 0.5) (mid-grey) • Dynamic lighting = enabled • Gourad shading mode • Solid polygon mode • Bilinear texture filtering