[英]Cairo Matrix equivillant of GlOrtho Matrix?
Given that I do something like this: 鉴于我做这样的事情:
void glOrtho( GLdouble left,
GLdouble right,
GLdouble bottom,
GLdouble top,
GLdouble nearVal,
GLdouble farVal);
and the result is: http://www.opengl.org/sdk/docs/man/xhtml/glOrtho.xml w could I achieve a matrix like this: 结果是: http : //www.opengl.org/sdk/docs/man/xhtml/glOrtho.xml w我可以实现如下矩阵:
http://cairographics.org/manual/cairo-matrix.html http://cairographics.org/manual/cairo-matrix.html
I tried this: 我尝试了这个:
cairo_matrix_t mat;
mat.xx = 2 / (right - left);
mat.yx = 0;
mat.xy = 2 / (top - bottom);
mat.yy = 0;
mat.x0 = 0;
mat.y0 = 0;
cairo_set_matrix(cr,&mat);
But it did not work. 但这没有用。 How could I acheive the same matrix that GlOrtho makes in Cairo? 我如何才能达到GlOrtho在开罗制作的矩阵? Thanks 谢谢
I don't know Cairo so I'll delete my answer if a better one comes. 我不知道开罗,所以如果有更好的答案,我会删除答案。
According to the docs of Cairo: 根据开罗的文档:
x_new = xx * x + xy * y + x0;
y_new = yx * x + yy * y + y0;
When you use OpenGL, the formula is like: ( m
being the matrix) 当您使用OpenGL时,公式类似于:( m
为矩阵)
x_new = m(1,1) * x + m(1,2) * y + m(1,3) * z + m(1,4)
y_new = m(2,1) * x + m(2,2) * y + m(2,3) * z + m(2,4)
z_new = m(3,1) * x + m(3,2) * y + m(3,3) * z + m(3,4)
(note that for the sake of simplicity I did not mention the fourth coordinate) (请注意,为简单起见,我没有提及第四坐标)
So what you have to do is simply match the two formulas: 因此,您要做的就是简单地匹配两个公式:
mat.xx = 2 / (right - left);
mat.yy = 2 / (top - bottom);
mat.xy = 0;
mat.yx = 0;
mat.x0 = -(right + left) / (right - left);
mat.y0 = -(top + bottom) / (top - bottom);
Please try this 请尝试这个
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