OpenGL glMatrixMode(GL_PROJECTION)和glMatrixMode(GL_MODELVIEW) [英] OpenGL glMatrixMode(GL_PROJECTION) vs glMatrixMode(GL_MODELVIEW)

问题描述

将 glRotatef()放在 glMatrixMode(GL_PROJECTION);

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glRotatef(red, green, blue);

并将 glRotatef()放在 glMatrixMode(GL_MODELVIEW);

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glRotatef(red, green, blue);

推荐答案

来自文档:

glMatrixMode()指定哪个矩阵是当前矩阵.

glMatrixMode() specifies which matrix is the current matrix.

GL_MODELVIEW - Applies subsequent matrix operations to the modelview matrix stack.

GL_PROJECTION - Applies subsequent matrix operations to the projection matrix stack.

它们是什么意思?

如果将当前矩阵模式设置为投影(例如glMatrixMode(GL_PROJECTION))，则应更改投影矩阵.当然，其中之一有望成为下一行:

If you set current matrix mode as projection (e.g glMatrixMode(GL_PROJECTION)), you are expected to change your projection matrix. Naturally, one of them are expected to be next line :

对于正投影:

• glOrtho(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble near, GLdouble far);
• gluOrtho2D(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top);

• glOrtho(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble near, GLdouble far);
• gluOrtho2D(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top);

对于透视投影:

• void glFrustum(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble near, GLdouble far);
• void gluPerspective(GLdouble fov, GLdouble aspect, GLdouble near, GLdouble far);

• void glFrustum(GLdouble left, GLdouble right, GLdouble bottom, GLdouble top, GLdouble near, GLdouble far);
• void gluPerspective(GLdouble fov, GLdouble aspect, GLdouble near, GLdouble far);

如果您将当前矩阵模式设置为modelView(例如glMatrixMode(GL_MODELVIEW))，则表示我在modelview矩阵中，并且我可以应用基本操作来转换对象，例如:

If you set current matrix mode as modelView(e.g glMatrixMode(GL_MODELVIEW)), you are saying that I am in the modelview matrix and I can apply basic operations to transform my objects like :

• glRotatef();
• glTranslatef();
• glScalef();

• glRotatef();
• glTranslatef();
• glScalef();

在您的问题中，如果在gl_projection之后而不是gl_modelview之后使用rotatef，则会旋转投影矩阵，这会破坏投影矩阵.

In your question if you use rotatef after gl_projection instead of gl_modelview, you rotate your projection matrix which would corrupt your projection matrix.

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