Define: glMatrixMode glLoadMatrix glLoadIdentity glPushMatrix glPopMatrix ..from opengl.org/sdk/docs..

[References]
1. "glMatrixMode"
2. "glLoadMatrix"

3. "glLoadIdentity"

4. "glPushMatrix, glPopMatrix"

glMatrixMode 

• glMatrixMode — specify which matrix is the current matrix

C Specification

• void glMatrixMode( GLenum mode);

Parameters
mode  

• Specifies which matrix stack is the target for subsequent matrix operations. 
• Three values are accepted: GL_MODELVIEW, GL_PROJECTION, and GL_TEXTURE. 
• The initial value is GL_MODELVIEW. 
• Additionally, if the ARB_imaging extension is supported, GL_COLOR is also accepted.

Description

• glMatrixMode sets the current matrix mode. mode can assume one of four values:
• GL_MODELVIEW
• Applies subsequent matrix operations to the modelview matrix stack.GL_PROJECTION
• Applies subsequent matrix operations to the projection matrix stack.GL_TEXTURE
• Applies subsequent matrix operations to the texture matrix stack.GL_COLOR
• Applies subsequent matrix operations to the color matrix stack.

To find out which matrix stack is currently the target of all matrix operations, call glGet with argument GL_MATRIX_MODE. The initial value is GL_MODELVIEW.

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glLoadMatrix 

• glLoadMatrix — replace the current matrix with the specified matrix

C Specification

• void glLoadMatrixd( const GLdouble * m);
• void glLoadMatrixf( const GLfloat * m);

Parameters
m

• Specifies a pointer to 16 consecutive values, which are used as the elements of a 4 × 4 column-major matrix.

Description

• glLoadMatrix replaces the current matrix with the one whose elements are specified by m. 
• The current matrix is the projection matrix, modelview matrix, or texture matrix, depending on the current matrix mode (see glMatrixMode).
• The current matrix, M, defines a transformation of coordinates. 
• For instance, assume M refers to the modelview matrix. If v = v0 v1 v2 v3 is the set of object coordinates of a vertex, and mpoints to an array of 16 single- or double-precision floating-point values m = m0 m1 ... m15 , then the modelview transformation M ⁡ v does the following:

• Mv = m0 m4 m8 m12 m1 m5 m9 m13 m2 m6 m10 m14 m3 m7 m11 m15 × v0 v1 v2 v3

• Projection and texture transformations are similarly defined.

Notes

While the elements of the matrix may be specified with single or double precision, the GL implementation may store or operate on these values in less than single precision.

glLoadIdentity

• glLoadIdentity — replace the current matrix with the identity matrix

C Specification

• void glLoadIdentity( void);

Description

• glLoadIdentity replaces the current matrix with the identity matrix. It is semantically equivalent to calling glLoadMatrix with the identity matrix
• 1 0 0 0 0 1 0 0 0 0 1 0 0 0 0 1
• but in some cases it is more efficient.

Errors

• GL_INVALID_OPERATION is generated if glLoadIdentity is executed between the execution of glBegin and the corresponding execution of glEnd.

Associated Gets

• glGet with argument GL_MATRIX_MODE
• glGet with argument GL_COLOR_MATRIX
• glGet with argument GL_MODELVIEW_MATRIX
• glGet with argument GL_PROJECTION_MATRIX
• glGet with argument GL_TEXTURE_MATRIX

glPushMatrix,glPopMatrix

• glPushMatrix — push and pop the current matrix stack

C Specification

• void glPushMatrix( void);

C Specification

• void glPopMatrix( void);

Description

• There is a stack of matrices for each of the matrix modes. 
• In GL_MODELVIEW mode, the stack depth is at least 32. 
• In the other modes, GL_COLOR, GL_PROJECTION, and GL_TEXTURE, the depth is at least 2. The current matrix in any mode is the matrix on the top of the stack for that mode.
• glPushMatrix pushes the current matrix stack down by one, duplicating the current matrix. That is, after a glPushMatrix call, the matrix on top of the stack is identical to the one below it.
• glPopMatrix pops the current matrix stack, replacing the current matrix with the one below it on the stack.
• Initially, each of the stacks contains one matrix, an identity matrix.
• It is an error to push a full matrix stack or to pop a matrix stack that contains only a single matrix. In either case, the error flag is set and no other change is made to GL state.

Errors

• GL_STACK_OVERFLOW is generated if glPushMatrix is called while the current matrix stack is full.
• GL_STACK_UNDERFLOW is generated if glPopMatrix is called while the current matrix stack contains only a single matrix.
• GL_INVALID_OPERATION is generated if glPushMatrix or glPopMatrix is executed between the execution of glBegin and the corresponding execution of glEnd.

Associated Gets

• glGet with argument GL_MATRIX_MODE
• glGet with argument GL_COLOR_MATRIX
• glGet with argument GL_MODELVIEW_MATRIX
• glGet with argument GL_PROJECTION_MATRIX
• glGet with argument GL_TEXTURE_MATRIX
• glGet with argument GL_COLOR_MATRIX_STACK_DEPTH
• glGet with argument GL_MODELVIEW_STACK_DEPTH
• glGet with argument GL_PROJECTION_STACK_DEPTH
• glGet with argument GL_TEXTURE_STACK_DEPTH
• glGet with argument GL_MAX_MODELVIEW_STACK_DEPTH
• glGet with argument GL_MAX_PROJECTION_STACK_DEPTH
• glGet with argument GL_MAX_TEXTURE_STACK_DEPTH

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