glGetProgramiv — return a parameter from a program object
void glGetProgramiv( | GLuint program, |
GLenum pname, | |
GLint *params) ; |
program
Specifies the program object to be queried.
pname
Specifies the object parameter. Accepted
symbolic names are
GL_DELETE_STATUS
,
GL_LINK_STATUS
,
GL_VALIDATE_STATUS
,
GL_INFO_LOG_LENGTH
,
GL_ATTACHED_SHADERS
,
GL_ACTIVE_ATTRIBUTES
,
GL_ACTIVE_ATTRIBUTE_MAX_LENGTH
,
GL_ACTIVE_UNIFORMS
,
GL_ACTIVE_UNIFORM_MAX_LENGTH
.
params
Returns the requested object parameter.
glGetProgramiv
returns in params
the value of a parameter for a specific program object. The following parameters are defined:
GL_DELETE_STATUS
params
returns
GL_TRUE
if
program
is currently flagged
for deletion, and GL_FALSE
otherwise.
GL_LINK_STATUS
params
returns
GL_TRUE
if the last link
operation on program
was
successful, and GL_FALSE
otherwise.
GL_VALIDATE_STATUS
params
returns
GL_TRUE
or if the last
validation operation on
program
was successful, and
GL_FALSE
otherwise.
GL_INFO_LOG_LENGTH
params
returns the
number of characters in the information log for
program
including the null
termination character (i.e., the size of the
character buffer required to store the information
log). If program
has no
information log, a value of 0 is
returned.
GL_ATTACHED_SHADERS
params
returns the
number of shader objects attached to
program
.
GL_ACTIVE_ATTRIBUTES
params
returns the
number of active attribute variables for
program
.
GL_ACTIVE_ATTRIBUTE_MAX_LENGTH
params
returns the
length of the longest active attribute name for
program
, including the null
termination character (i.e., the size of the
character buffer required to store the longest
attribute name). If no active attributes exist, 0 is
returned.
GL_ACTIVE_UNIFORMS
params
returns the
number of active uniform variables for
program
.
GL_ACTIVE_UNIFORM_MAX_LENGTH
params
returns the
length of the longest active uniform variable name
for program
, including the
null termination character (i.e., the size of the
character buffer required to store the longest
uniform variable name). If no active uniform
variables exist, 0 is returned.
GL_INVALID_ENUM
is generated if pname
is not an accepted value.
GL_INVALID_VALUE
is generated if program
is not a value generated by OpenGL.
GL_INVALID_OPERATION
is generated if program
does not refer to a program object.
glGetActiveAttrib
with argument program
glGetActiveUniform
with argument program
glGetAttachedShaders
with argument program
glGetProgramInfoLog
with argument program
GLuint vshader = glCreateShader(GL_VERTEX_SHADER); glShaderSource(vshader, 1, &vertex_shader_source, NULL); // vertex_shader_source is a GLchar* containing glsl shader source code glCompileShader(vshader); GLint vertex_compiled; glGetShaderiv(vshader, GL_COMPILE_STATUS, &vertex_compiled); if (vertex_compiled != GL_TRUE) { GLsizei log_length = 0; GLchar message[1024]; glGetShaderInfoLog(vshader, 1024, &log_length, message); // Write the error to a log } GLuint fshader = glCreateShader(GL_FRAGMENT_SHADER); glShaderSource(fshader, 1, &fragment_shader_source, NULL); // fragment_shader_source is a GLchar* containing glsl shader source code glCompileShader(fshader); GLint fragment_compiled; glGetShaderiv(fshader, GL_COMPILE_STATUS, &fragment_compiled); if (fragment_compiled != GL_TRUE) { GLsizei log_length = 0; GLchar message[1024]; glGetShaderInfoLog(fshader, 1024, &log_length, message); // Write the error to a log } GLuint program = glCreateProgram(); // This step is unnecessary if you use the location specifier in your shader // e.g. layout (location = 0) in vec3 position; glBindAttribLocation(program, 0, "position"); // The index passed into glBindAttribLocation is glBindAttribLocation(program, 1, "texcoord"); // used by glEnableVertexAttribArray. "position" glBindAttribLocation(program, 2, "normal"); // "texcoord" "normal" and "color" are the names of the glBindAttribLocation(program, 3, "color"); // respective inputs in your fragment shader. glAttachShader(program, vshader); glAttachShader(program, fshader); glLinkProgram(program); GLint program_linked; glGetProgramiv(program, GL_LINK_STATUS, &program_linked); if (program_linked != GL_TRUE) { GLsizei log_length = 0; GLchar message[1024]; glGetProgramInfoLog(program, 1024, &log_length, message); // Write the error to a log }
// The index returned from these GLint functions gets passed to glEnableVertexAttribArray during rendering. GLint position_attrib_index = glGetAttribLocation(program, "position"); // program is what is returned by glCreateProgram. GLint texcoord_attrib_index = glGetAttribLocation(program, "texcoord"); GLint normal_attrib_index = glGetAttribLocation(program, "normal"); GLint color_attrib_index = glGetAttribLocation(program, "color"); glBindFragDataLocation(program, 0, "output_color"); // "output_color" is an output value in your vertex shader and an input value in your fragment shader. GLint num_uniforms; glGetProgramiv(program, GL_ACTIVE_UNIFORMS, &num_uniforms); GLchar uniform_name[256]; GLsizei length; GLint size; GLenum type; for (int i = 0; i < num_uniforms; i++) { glGetActiveUniform(program, i, sizeof(uniform_name), &length, &size, &type, uniform_name); // ... save this uniform data so it can be used during rendering }
glAttachShader, glCreateProgram, glDeleteProgram, glGetShaderiv, glLinkProgram, glValidateProgram
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