Vertex Specification
In "Modern" OpenGL
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Prof. David Bernstein
James Madison University
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Computer Science Department
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bernstdh@jmu.edu
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Important Concepts
- Vertex Stream:
- The stream of data values that define the vertices
- Vertex Attributes:
- A description of the elements in the vertex stream
- Primitive:
- The shape that is encapsulated by the vertex stream
The Vertex Stream
- Makeup:
- Everything that is needed to encapsulate a collection
of vertices (e.g., positions, colors, normals)
- Organization:
- Can be interleaved or not (e.g., the position of the
first vertex can be followed by the color of the first
vertex or the positions of all vertices can come
first, followed by the colors of all vertices)
The Vertex Stream (cont.)
A Scene Object Consisting of Two Triangles with a Non-Interleaved Stream
openglexamples/modern/multiple.cpp
(Fragment: stream)
The Vertex Stream (cont.)
A Scene Object Consisting of Two Triangles with an Interleaved Stream
openglexamples/modern/interleaved.cpp
(Fragment: stream)
Vertex Specification
- Vertex Array Objects:
- Describe the data associated with each vertex
- Vertex Buffer Objects:
- Store the data associated with each vertex
Vertex Buffer Objects
- Buffer Objects:
- Store an array of unformatted memory allocated by the
OpenGL context (typically on the GPU)
- Vertex Buffer Objects (VBOs):
- A buffer object that is used as a source for vertex data
Vertex Buffer Objects (cont.)
- Creation:
-
void glGenBuffers(GLsizei n,
GLuint* buffers) where
n
is the inbound number of buffers to create
and
buffers
is the outbound array of
names/handles/IDs
- Deletion:
-
void glDeleteBuffers(GLsizei n,
const GLuint* buffers)
where
n
is the inbound number of buffers to create
and
buffers
is the inbound array of
names/handles/IDs to delete
- Setting State:
-
void glBindBuffer(enum target,
uint bufferName)
binds the buffer object to the context so its state can be changed
(where
target
is
typically GL_ARRAY_BUFFER)
- Subsequent calls to
glBufferStorage(),
glBufferData(), glClearBufferData(), etc...
then change the state
Vertex Buffer Objects (cont.)
The VBOs for the Non-Interleaved Stream
openglexamples/modern/multiple.cpp
(Fragment: vbo)
Vertex Buffer Objects (cont.)
The VBO for the Interleaved Stream
openglexamples/modern/interleaved.cpp
(Fragment: vbo)
Vertex Array Objects (VAOs)
- Recall:
- Purpose of VAOs:
- Store all of the state needed by vertices (including the
format and the VBOs)
Vertex Array Objects (VAOs)
- Creation:
-
void glGenVertexArrays(GLsizei n,
GLuint* arrays);
where
n
is the inbound number of buffers to create
and
arrays
is the outbound array of
names/handles/IDs
- Deletion:
-
void glDeleteVertexArrays(GLsizei n, const
GLuint *arrays); where
n
is the inbound number of buffers to create
and
arrays
is the inbound array of
names/handles/IDs to delete
- Setting State:
-
void glBindVertexArray(GLuint array);
binds the VAO to the context so it's state can be changed
-
void glEnableVertexAttribArray(GLuint index);
allows the attribute numbered index to be changed
-
glVertexAttribPointer() can then be used to
set the format of the VBO and associate the currently bound VBO
with the currently bound VBA
-
void glDisableVertexAttribArray(
GLuint index);
prevents the attribute numbered
index
from being
changed
Vertex Array Objects (cont.)
The VAOs for the Non-Interleaved Stream
openglexamples/modern/multiple.cpp
(Fragment: vao)
Vertex Array Objects (cont.)
The VAOs for the Interleaved Stream
openglexamples/modern/interleaved.cpp
(Fragment: vao)
There's Always More to Learn