Model Primitive

The model primitive supports model articulations, which allow different parts of the model to be rotated, scaled, and/or translated. If the model supports articulations, they can be accessed through the ModelPrimitive'sArticulations property.

An example of how to modify a model's articulations is shown below.

The model primitive without modifying the spin ModelTransformation of the propeller's ModelArticulation:

The same model with the spin of the propellers modified to be 135 degrees:

[C#]

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// Create the model and set the position. IAgStkGraphicsModelPrimitive model = manager.Initializers.ModelPrimitive.InitializeWithStringUri(modelUri); Array position = new object[] { 36, -116.75, 25000.0 }; model.SetPositionCartographic("Earth", ref position); // Modify the roll and yaw of the entire model so that the model appears to be parallel // with the horizon. This method is only to demonstrate how articulations can be used. // the preferred method is to set the model's orientation. model.Articulations.GetByName("Commuter").GetByName("Roll").CurrentValue = 234; model.Articulations.GetByName("Commuter").GetByName("Yaw").CurrentValue = -25; // Modify the spin of the propellers. model.Articulations.GetByName("props").GetByName("Spin").CurrentValue = 135;

The Articulations property of the ModelPrimitive is an instance of ModelArticulationCollection. ModelArticulationCollection contains a collection of ModelArticulations. ModelArticulation contains a collection of ModelTransformations. Both the ModelArticulationCollection and ModelArticulation classes accept an integer index to access its values. Use the ModelTransformation.CurrentValue property to set the value of the transformation as shown in the code above. The Type of transformation can also be retrieved using the ModelTransformation.Type property which returns a value of the ModelTransformationType enumeration.

Collada models also support the ColladaFX framework, which allows users to write GLSL code to calculate vertex positions, pixel colors, etc. This allows for models to exhibit lighting properties of materials such as metal, glass, plastic, etc. ColladaFX also allows changing OpenGL States, use of all supported OpenGL Texture types (1D, 2D, 3D, cubemap, rectangle, shadow), and render to texture for use with multipass rendering techniques.

Satellite that uses a metallic BRDF based on the work of Ashikhmin and Shirley. This example can be seen in the GraphicsHowTo example under "Primitives" -> "Models" -> "Draw a Collada model with user defined lighting"

Within your shader code, you have access to scene data that is useful for shading your model. We refer to these as Preset Uniforms because they are accessed as uniform variables in your vertex or fragment shader. These variables must be declared as uniforms and then can be used. Here is an example using STK Engine's animation time to move a vertex.

[GLSL]

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uniform float agi_Time; uniform float fullOffset; // Vertex Shader that oscillates from position to position+fullOffset along the Z axis. void main() {      // Get fractional part of time      float t = fract(agi_Time);      // Move apply modelview and projection      vec4 pos = gl_ModelViewProjectionMatrix * gl_Vertex;      // Move vertex a certain percentage of offset      pos.z += fullOffset * t;      // Set position      gl_Position = pos; }

Preset Uniforms

Preset Uniform	Type	Description
agi_ActiveLights	bool[gl_MaxLights]	Light i is active if agi_ActiveLights[i] is true and inactive if false. Light properties can be accessed through gl_LightSources.
agi_CameraPosition	vec3	Position of the camera relative to the model's reference frame.
agi_CentralBodyDepthTexture0, agi_CentralBodyDepthTexture1, ..., agi_CentralBodyDepthTexture7	sampler2D	A texture that contains the depth values after rendering the Central Body. The number binds the texture to a particular texture unit. See example image below.
agi_LightingEnabled	float	1 if lighting is enabled and 0 otherwise
agi_LODGeometricToleranceOverDistance	float	When multiplied by the distance from the vertex or fragment to the viewer, the result is the geometric error in world space.
agi_LODNegativeGeometricToleranceOverDistance	float	Negative of agi_LODGeometricToleranceOverDistance
agi_ModelViewMatrix	mat4	Modelview matrix
agi_ModelViewMatrixRelativeToCameraPosition	mat4	Modelview matrix relative to the camera position
agi_ModelViewMatrixRelativeToPrimitiveCenter	mat4	Modelview matrix relative to the model's center
agi_ModelViewProjectionMatrix	mat4	Modelview projection matrix
agi_ModelViewProjectionMatrixRelativeToCameraPosition	mat4	Modelview projection matrix relative to the camera position
agi_ModelViewProjectionMatrixRelativeToPrimitiveCenter	mat4	Modelview projection matrix relative to the model's center
agi_OrthographicProjectionMatrix	mat4	Orthographic projection matrix
agi_PerspectiveProjectionMatrix	mat4	Perspective projection matrix
agi_PrimitiveBoundingSphere	vec4	The model's bounding sphere relative to the model's reference frame. The structure is xyz components are the position and w is the radius in meters.
agi_PrimitiveBoundingSphereRelativeToCameraPosition	vec4	The model's bounding sphere relative to the camera position. The structure is xyz components are the position and w is the radius in meters.
agi_PrimitiveColor	vec4	The color of the primitive
agi_SnapshotPixelScale	float	Scale for when rendering high resolution snap shots. Otherwise it is 1.
agi_TerrainSilhouetteTexture0, agi_TerrainSilhouetteTexture1, ..., agi_TerrainSilhouetteTexture7	sampler2D	A texture that contains the silhouette of the terrain. The number binds the texture to a particular texture unit. See example image below.
agi_Time	float	Number of seconds since the time specified to StartTime property.
agi_Viewport	vec4	The viewport in the format (left, bottom, width, height)

Central Body rendered normally	Central Body Depth Texture

Example of Terrain Silhouette Texture

OpenGL States

Supported OpenGL States

ColladaFX Element	OpenGL State	Notes
alpha_func	glAlphaFunc
alpha_test_enable	glEnable/glDisable with GL_ALPHA_TEST
blend_color	glBlendColor
blend_enable	glEnable/glDisable with GL_BLEND
blend_equation	glBlendEquation
blend_equation_separate	glBlendEquationSeparate	Requires OpenGL 2.0
blend_func	glBlendFunc
blend_func_separate	glBlendFuncSeparate	Requires OpenGL 1.4
color_mask	glColorMask
cull_face	glCullFace
cull_face_enable	glEnable/glDisable with GL_CULL_FACE
depth_clamp_enable	glEnable/glDisable with GL_DEPTH_CLAMP_NV	Requires GL 3.2 or GL_ARB_depth_clamp
depth_func	glDepthFunc
depth_mask	glDepthMask
depth_range	glDepthRange
depth_test_enable	glEnable/glDisable with GL_DEPTH_TEST
fog_color	glFogfv with GL_FOG_COLOR
fog_density	glFogf with GL_FOG_DENSITY
fog_enable	glEnable/glDisable with GL_FOG
fog_end	glFogf with GL_FOG_END
fog_mode	glFogi with GL_FOG_MODE
fog_start	glFogf with GL_FOG_START
front_face	glFrontFace
line_smooth_enable	glEnable/glDisable with GL_LINE_SMOOTH
line_stipple	glLineStipple
line_stipple_enable	glEnable/glDisable with GL_LINE_STIPPLE
line_width	glLineWidth
point_size	glPointSize
point_smooth_enable	glEnable/glDisable with GL_POINT_SMOOTH
polygon_mode	glPolygonMode	Only FRONT_AND_BACK
polygon_offset	glPolygonOffset
polygon_offset_fill_enable	glEnable/glDisable with GL_POLYGON_OFFSET_FILL
scissor	glScissor
scissor_test_enable	glEnable/glDisable with GL_SCISSOR_TEST
shade_model	glShadeModel
stencil_func	glStencilFunc
stencil_func_separate	glStencilFuncSeparate	Requires OpenGL 2.0
stencil_mask	glStencilMask
stencil_mask_separate	glStencilMaskSeparate	Requires OpenGL 2.0
stencil_op	glStencilOp
stencil_op_separate	glStencilOpSeparate	Requires OpenGL 2.0
stencil_test_enable	glEnable/glDisable with GL_STENCIL_TEST
texture1D	glBindTexture with GL_TEXTURE_1D
texture2D	glBindTexture with GL_TEXTURE_2D
texture3D	glBindTexture with GL_TEXTURE_3D
textureCUBE	glBindTexture with GL_TEXTURE_CUBE_MAP	Requires OpenGL 1.3
textureDEPTH	glBindTexture with GL_TEXTURE_2D	Used for depth textures.
textureRECT	glBindTexture with GL_TEXTURE_RECTANGLE_ARB

Unsupported OpenGL States

ColladaFX Element	Notes
auto_normal_enable
clip_plane	Can be emulated in the fragment shader. Removed from OpenGL 3.2 core.
clip_plane_enable	Can be emulated in the fragment shader. Removed from OpenGL 3.2 core.
color_logic_op_enable	Rarely used.
color_material	Can be emulated in the fragment shader by implementing a BRDF. Removed from OpenGL 3.2 core.
color_material_enable	Can be emulated in the fragment shader by implementing a BRDF. Removed from OpenGL 3.2 core.
depth_bounds	Only affects performance, not the visual output. Not in core GL, requires EXT_depth_bounds_test.
depth_bounds_enable	Only affects performance, not the visual output. Not in core GL, requires EXT_depth_bounds_test.
dither_enable	Rarely used.
light_ambient	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
light_constant_attenuation	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
light_diffuse	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
light_enable	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
light_linear_attenuation	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
light_model_ambient	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
light_model_color_control	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
light_model_local_viewer_enable	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
light_model_two_side_enable	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
light_position	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
light_quadratic_attenuation	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
light_specular	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
light_spot_cutoff	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
light_spot_direction	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
light_spot_exponent	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
lighting_enable	Can be emulated in fragment shader. Fixed function lighting was removed from OpenGL 3.2 core.
logic_op	Rarely used.
logic_op_enable	Rarely used.
material_ambient	Can be emulated in the fragment shader by implementing a BRDF. Removed from OpenGL 3.2 core.
material_diffuse	Can be emulated in the fragment shader by implementing a BRDF. Removed from OpenGL 3.2 core.
material_emission	Can be emulated in the fragment shader by implementing a BRDF. Removed from OpenGL 3.2 core.
material_shininess	Can be emulated in the fragment shader by implementing a BRDF. Removed from OpenGL 3.2 core.
material_specular	Can be emulated in the fragment shader by implementing a BRDF. Removed from OpenGL 3.2 core.
model_view_matrix	Can be emulated in the shader. Removed from OpenGL 3.2 core.
multisample_enable	Requires an OpenGL context be created with multisample buffers, which is currently not supported in STK Engine.
normalize_enable	This is always enabled.
point_distance_attenuation
point_fade_threshold_size
point_size_enable
point_size_max
point_size_min
polygon_offset_line_enable
polygon_offset_point_enable
polygon_smooth_enable
projection_matrix	Can be emulated in the shader. Removed from OpenGL 3.2 core.
sample_alpha_to_coverage_enable	Requires an OpenGL context be created with multisample buffers, which is currently not supported in STK Engine.
sample_alpha_to_one_enable	Requires an OpenGL context be created with multisample buffers, which is currently not supported in STK Engine.
sample_coverage
sample_coverage_enable
texture_env_color	Can be emulated in the fragment shader. Removed from OpenGL 3.2 core.
texture_env_color	Can be emulated in the fragment shader. Removed from OpenGL 3.2 core.
texture_pipeline	GLES profile only. GLSL is currently the only supported profile.
texture1D_enable	This isn't required when using a texture in a shader. Removed from OpenGL 3.2 core
texture2D_enable	This isn't required when using a texture in a shader. Removed from OpenGL 3.2 core
texture3D_enable	This isn't required when using a texture in a shader. Removed from OpenGL 3.2 core
textureCUBE_enable	This isn't required when using a texture in a shader. Removed from OpenGL 3.2 core
textureDEPTH_enable	This isn't required when using a texture in a shader. Removed from OpenGL 3.2 core
textureRECT_enable	This isn't required when using a texture in a shader. Removed from OpenGL 3.2 core

Resources
Collada 1.4.1 Specification
GLSL Specification
GLSL Tutorial
BRDF explanation and examples