Graphics Reference
In-Depth Information
The built-in constants describe the following maximum terms:
•
gl_MaxVertexAttribs
is the maximum number of vertex attributes
that can be specified. The minimum value supported by all ES 3.0
implementations is 16.
•
gl_MaxVertexUniformVectors
is the maximum number of
vec4
uniform entries that can be used inside a vertex shader.
The minimum value supported by all ES 3.0 implementations is
256
vec4
entries. The number of
vec4
uniform entries that can
actually be used by a developer can vary from one implementation
to another and from one vertex shader to another. For example,
some implementations might count user-specified literal values
used in a vertex shader against the uniform limit. In other cases,
implementation-specific uniforms (or constants) might need to be
included depending on whether the vertex shader makes use of any
built-in transcendental functions. There currently is no mechanism
that an application can use to find the number of uniform entries
that it can use in a particular vertex shader. The vertex shader
compilation will fail and the compile log might provide specific
information with regard to number of uniform entries being
used. However, the information returned by the compile log is
implementation specific. We provide some guidelines in this chapter
to help maximize the use of vertex uniform entries available in a
vertex shader.
•
gl_MaxVertexOutputVectors
is the maximum number of output
vectors—that is, the number of
vec4
entries that can be output
by a vertex shader. The minimum value supported by all ES 3.0
implementations is 16
vec4
entries.
•
gl_MaxVertexTextureImageUnits
is the maximum number of
texture units available in a vertex shader. The minimum value is 16.
•
gl_MaxCombinedTextureImageUnits
is the sum of the maximum
number of texture units available in the vertex + fragment shaders.
The minimum value is 32.
The values specified for each built-in constant are the minimum values
that must be supported by all OpenGL ES 3.0 implementations. It is
possible that implementations might support values greater than the
minimum values described. The actual supported values can be queried
using the following code:
GLint maxVertexAttribs, maxVertexUniforms, maxVaryings;
GLint maxVertexTextureUnits, maxCombinedTextureUnits;
