Cogl.Attribute¶

Subclasses:: None

Methods¶

Inherited:: Cogl.Object (2)

class	`new` (attribute_buffer, name, stride, offset, components, type)
class	`new_const_1f` (context, name, value)
class	`new_const_2f` (context, name, component0, component1)
class	`new_const_2fv` (context, name, value)
class	`new_const_2x2fv` (context, name, matrix2x2, transpose)
class	`new_const_3f` (context, name, component0, component1, component2)
class	`new_const_3fv` (context, name, value)
class	`new_const_3x3fv` (context, name, matrix3x3, transpose)
class	`new_const_4f` (context, name, component0, component1, component2, component3)
class	`new_const_4fv` (context, name, value)
class	`new_const_4x4fv` (context, name, matrix4x4, transpose)
	`get_buffer` ()
	`get_normalized` ()
	`set_buffer` (attribute_buffer)
	`set_normalized` (normalized)

Virtual Methods¶

None

Fields¶

None

Class Details¶

class Cogl.Attribute¶

Bases:: Cogl.Object
Abstract:: No

classmethod new(attribute_buffer, name, stride, offset, components, type)¶

Parameters:

attribute_buffer (Cogl.AttributeBuffer) – The Cogl.AttributeBuffer containing the actual attribute data
name (str) – The name of the attribute (used to reference it from GLSL)
stride (int) – The number of bytes to jump to get to the next attribute value for the next vertex. (Usually sizeof (MyVertex))
offset (int) – The byte offset from the start of attribute_buffer for the first attribute value. (Usually offsetof (MyVertex, component0)
components (int) – The number of components (e.g. 4 for an rgba color or 3 for and (x,y,z) position)
type (Cogl.AttributeType) – FIXME

Returns:

A newly allocated Cogl.Attribute describing the layout for a list of attribute values stored in array.

Return type:

Cogl.Attribute

Describes the layout for a list of vertex attribute values (For example, a list of texture coordinates or colors).

The name is used to access the attribute inside a GLSL vertex shader and there are some special names you should use if they are applicable:

“cogl_position_in” (used for vertex positions)
“cogl_color_in” (used for vertex colors)
“cogl_tex_coord0_in”, “cogl_tex_coord1”, … (used for vertex texture coordinates)
“cogl_normal_in” (used for vertex normals)
“cogl_point_size_in” (used to set the size of points per-vertex. Note this can only be used if %COGL_FEATURE_ID_POINT_SIZE_ATTRIBUTE is advertised and Cogl.Pipeline.set_per_vertex_point_size() is called on the pipeline.

The attribute values corresponding to different vertices can either be tightly packed or interleaved with other attribute values. For example it’s common to define a structure for a single vertex like:

typedef struct
{
  float x, y, z; /<!-- -->* position attribute *<!-- -->/
  float s, t; /<!-- -->* texture coordinate attribute *<!-- -->/
} MyVertex;

And then create an array of vertex data something like:

MyVertex vertices[100] = { .... }

In this case, to describe either the position or texture coordinate attribute you have to move sizeof (MyVertex) bytes to move from one vertex to the next. This is called the attribute stride. If you weren’t interleving attributes and you instead had a packed array of float x, y pairs then the attribute stride would be (2 * sizeof (float)). So the stride is the number of bytes to move to find the attribute value of the next vertex.

Normally a list of attributes starts at the beginning of an array. So for the MyVertex example above the offset is the offset inside the MyVertex structure to the first component of the attribute. For the texture coordinate attribute the offset would be offsetof (MyVertex, s) or instead of using the offsetof macro you could use sizeof (float) * 3. If you’ve divided your array into blocks of non-interleved attributes then you will need to calculate the offset as the number of bytes in blocks preceding the attribute you’re describing.

An attribute often has more than one component. For example a color is often comprised of 4 red, green, blue and alpha components, and a position may be comprised of 2 x and y components. You should aim to keep the number of components to a minimum as more components means more data needs to be mapped into the GPU which can be a bottlneck when dealing with a large number of vertices.

Finally you need to specify the component data type. Here you should aim to use the smallest type that meets your precision requirements. Again the larger the type then more data needs to be mapped into the GPU which can be a bottlneck when dealing with a large number of vertices.

New in version 1.4.

classmethod new_const_1f(context, name, value)¶

Parameters:

context (Cogl.Context) – A Cogl.Context
name (str) – The name of the attribute (used to reference it from GLSL)
value (float) – The constant value for the attribute

Returns:

A newly allocated Cogl.Attribute representing the given constant value.

Return type:

Cogl.Attribute

Creates a new, single component, attribute whose value remains constant across all the vertices of a primitive without needing to duplicate the value for each vertex.

The constant value is a single precision floating point scalar which should have a corresponding declaration in GLSL code like:

[| attribute float name; |]

classmethod new_const_2f(context, name, component0, component1)¶

Parameters:

context (Cogl.Context) – A Cogl.Context
name (str) – The name of the attribute (used to reference it from GLSL)
component0 (float) – The first component of a 2 component vector
component1 (float) – The second component of a 2 component vector

Returns:

A newly allocated Cogl.Attribute representing the given constant vector.

Return type:

Cogl.Attribute

Creates a new, 2 component, attribute whose value remains constant across all the vertices of a primitive without needing to duplicate the value for each vertex.

The constants (component0, component1) represent a 2 component float vector which should have a corresponding declaration in GLSL code like:

[| attribute vec2 name; |]

classmethod new_const_2fv(context, name, value)¶

Parameters:

context (Cogl.Context) – A Cogl.Context
name (str) – The name of the attribute (used to reference it from GLSL)
value (float) – A pointer to a 2 component float vector

Returns:

A newly allocated Cogl.Attribute representing the given constant vector.

Return type:

Cogl.Attribute

Creates a new, 2 component, attribute whose value remains constant across all the vertices of a primitive without needing to duplicate the value for each vertex.

The constants (value[0], value[1]) represent a 2 component float vector which should have a corresponding declaration in GLSL code like:

[| attribute vec2 name; |]

classmethod new_const_2x2fv(context, name, matrix2x2, transpose)¶

Parameters:

context (Cogl.Context) – A Cogl.Context
name (str) – The name of the attribute (used to reference it from GLSL)
matrix2x2 (float) – A pointer to a 2 by 2 matrix
transpose (int) – Whether the matrix should be transposed on upload or not

Returns:

A newly allocated Cogl.Attribute representing the given constant matrix.

Return type:

Cogl.Attribute

Creates a new matrix attribute whose value remains constant across all the vertices of a primitive without needing to duplicate the value for each vertex.

matrix2x2 represent a square 2 by 2 matrix specified in column-major order (each pair of consecutive numbers represents a column) which should have a corresponding declaration in GLSL code like:

[| attribute mat2 name; |]

If transpose is True then all matrix components are rotated around the diagonal of the matrix such that the first column becomes the first row and the second column becomes the second row.

classmethod new_const_3f(context, name, component0, component1, component2)¶

Parameters:

context (Cogl.Context) – A Cogl.Context
name (str) – The name of the attribute (used to reference it from GLSL)
component0 (float) – The first component of a 3 component vector
component1 (float) – The second component of a 3 component vector
component2 (float) – The third component of a 3 component vector

Returns:

A newly allocated Cogl.Attribute representing the given constant vector.

Return type:

Cogl.Attribute

Creates a new, 3 component, attribute whose value remains constant across all the vertices of a primitive without needing to duplicate the value for each vertex.

The constants (component0, component1, component2) represent a 3 component float vector which should have a corresponding declaration in GLSL code like:

[| attribute vec3 name; |]

unless the built in name “cogl_normal_in” is being used where no explicit GLSL declaration need be made.

classmethod new_const_3fv(context, name, value)¶

Parameters:

context (Cogl.Context) – A Cogl.Context
name (str) – The name of the attribute (used to reference it from GLSL)
value (float) – A pointer to a 3 component float vector

Returns:

A newly allocated Cogl.Attribute representing the given constant vector.

Return type:

Cogl.Attribute

Creates a new, 3 component, attribute whose value remains constant across all the vertices of a primitive without needing to duplicate the value for each vertex.

The constants (value[0], value[1], value[2]) represent a 3 component float vector which should have a corresponding declaration in GLSL code like:

[| attribute vec3 name; |]

unless the built in name “cogl_normal_in” is being used where no explicit GLSL declaration need be made.

classmethod new_const_3x3fv(context, name, matrix3x3, transpose)¶

Parameters:

context (Cogl.Context) – A Cogl.Context
name (str) – The name of the attribute (used to reference it from GLSL)
matrix3x3 (float) – A pointer to a 3 by 3 matrix
transpose (int) – Whether the matrix should be transposed on upload or not

Returns:

A newly allocated Cogl.Attribute representing the given constant matrix.

Return type:

Cogl.Attribute

Creates a new matrix attribute whose value remains constant across all the vertices of a primitive without needing to duplicate the value for each vertex.

matrix3x3 represent a square 3 by 3 matrix specified in column-major order (each triple of consecutive numbers represents a column) which should have a corresponding declaration in GLSL code like:

[| attribute mat3 name; |]

If transpose is True then all matrix components are rotated around the diagonal of the matrix such that the first column becomes the first row and the second column becomes the second row etc.

classmethod new_const_4f(context, name, component0, component1, component2, component3)¶

Parameters:

context (Cogl.Context) – A Cogl.Context
name (str) – The name of the attribute (used to reference it from GLSL)
component0 (float) – The first component of a 4 component vector
component1 (float) – The second component of a 4 component vector
component2 (float) – The third component of a 4 component vector
component3 (float) – The fourth component of a 4 component vector

Returns:

A newly allocated Cogl.Attribute representing the given constant vector.

Return type:

Cogl.Attribute

Creates a new, 4 component, attribute whose value remains constant across all the vertices of a primitive without needing to duplicate the value for each vertex.

The constants (component0, component1, component2, constant3) represent a 4 component float vector which should have a corresponding declaration in GLSL code like:

[| attribute vec4 name; |]

unless one of the built in names “cogl_color_in”, “cogl_tex_coord0_in or “cogl_tex_coord1_in” etc is being used where no explicit GLSL declaration need be made.

classmethod new_const_4fv(context, name, value)¶

Parameters:

context (Cogl.Context) – A Cogl.Context
name (str) – The name of the attribute (used to reference it from GLSL)
value (float) – A pointer to a 4 component float vector

Returns:

A newly allocated Cogl.Attribute representing the given constant vector.

Return type:

Cogl.Attribute

Creates a new, 4 component, attribute whose value remains constant across all the vertices of a primitive without needing to duplicate the value for each vertex.

The constants (value[0], value[1], value[2], value[3]) represent a 4 component float vector which should have a corresponding declaration in GLSL code like:

[| attribute vec4 name; |]

unless one of the built in names “cogl_color_in”, “cogl_tex_coord0_in or “cogl_tex_coord1_in” etc is being used where no explicit GLSL declaration need be made.

classmethod new_const_4x4fv(context, name, matrix4x4, transpose)¶

Parameters:

context (Cogl.Context) – A Cogl.Context
name (str) – The name of the attribute (used to reference it from GLSL)
matrix4x4 (float) – A pointer to a 4 by 4 matrix
transpose (int) – Whether the matrix should be transposed on upload or not

Returns:

A newly allocated Cogl.Attribute representing the given constant matrix.

Return type:

Cogl.Attribute

Creates a new matrix attribute whose value remains constant across all the vertices of a primitive without needing to duplicate the value for each vertex.

matrix4x4 represent a square 4 by 4 matrix specified in column-major order (each 4-tuple of consecutive numbers represents a column) which should have a corresponding declaration in GLSL code like:

[| attribute mat4 name; |]

If transpose is True then all matrix components are rotated around the diagonal of the matrix such that the first column becomes the first row and the second column becomes the second row etc.

get_buffer()¶

Returns:: the Cogl.AttributeBuffer that was set with Cogl.Attribute.set_buffer() or Cogl.Attribute.new().
Return type:: Cogl.AttributeBuffer

New in version 1.10.

get_normalized()¶

Returns:: the value of the normalized property set with Cogl.Attribute.set_normalized().
Return type:: int

New in version 1.10.

set_buffer(attribute_buffer)¶

Parameters:: attribute_buffer (Cogl.AttributeBuffer) – A Cogl.AttributeBuffer

Sets a new Cogl.AttributeBuffer for the attribute.

New in version 1.10.

set_normalized(normalized)¶

Parameters:: normalized (int) – The new value for the normalized property.

Sets whether fixed point attribute types are mapped to the range 0→1. For example when this property is True and a Cogl.AttributeType.UNSIGNED_BYTE type is used then the value 255 will be mapped to 1.0.

The default value of this property depends on the name of the attribute. For the builtin properties cogl_color_in and cogl_normal_in it will default to True and for all other names it will default to False.

New in version 1.10.