glGetProgramiv — Returns 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.
glGetProgram
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.
glGetProgram
is available only if the GL version is 2.0 or greater.
If an error is generated, no change is made to the contents of params
.
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.
GL_INVALID_ENUM
is generated if pname
is not an accepted value.
GL_INVALID_OPERATION
is generated if glGetProgram
is executed between the execution of glBegin and the corresponding execution of glEnd.
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, glGetShader, glLinkProgram, glValidateProgram
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