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[clip-stack] tidy up transform_point() code

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I was originally expecting the code not to handle offset viewports or
viewports with a different size to the framebuffer, but it turns out the
code worked fine.  In the process though I think I made the code slightly
more readable.
This commit is contained in:
Robert Bragg 2009-10-21 23:22:45 +01:00
parent 78ee3f71b2
commit 0f86470eef
1 changed files with 20 additions and 10 deletions
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30
cogl/cogl-clip-stack.c
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@ -155,13 +155,18 @@ cogl_clip_push_window_rect (float x_offset,
clip_state->stack_dirty = TRUE;
}
/* Scale from OpenGL <-1,1> coordinates system to window coordinates
* <0,window-size> with (0,0) being top left. */
#define VIEWPORT_SCALE_X(x, w, width, origin) \
((((((x) / (w)) + 1.0) / 2) * (width)) + (origin))
#define VIEWPORT_SCALE_Y(y, w, height, origin) \
((height) - (((((y) / (w)) + 1.0) / 2) * (height)) + (origin))
/* Scale from OpenGL normalized device coordinates (ranging from -1 to 1)
* to Cogl window/draw-buffer coordinates (ranging from 0 to buffer-size) with
* (0,0) being top left. */
#define VIEWPORT_TRANSFORM_X(x, vp_origin_x, vp_width) \
( ( ((x) + 1.0) * ((vp_width) / 2.0) ) + (vp_origin_x) )
/* Note: for Y we first flip all coordinates around the X axis while in
* normalized device coodinates */
#define VIEWPORT_TRANSFORM_Y(y, vp_origin_y, vp_height) \
( ( ((-(y)) + 1.0) * ((vp_height) / 2.0) ) + (vp_origin_y) )
/* Transform a homogeneous vertex position from model space to Cogl
* window coordinates (with 0,0 being top left) */
static void
transform_point (CoglMatrix *matrix_mv,
CoglMatrix *matrix_p,
@ -172,14 +177,19 @@ transform_point (CoglMatrix *matrix_mv,
float z = 0;
float w = 1;
/* Apply the model view matrix */
/* Apply the modelview matrix transform */
cogl_matrix_transform_point (matrix_mv, x, y, &z, &w);
/* Apply the projection matrix */
/* Apply the projection matrix transform */
cogl_matrix_transform_point (matrix_p, x, y, &z, &w);
/* Perform perspective division */
*x /= w;
*y /= w;
/* Apply viewport transform */
*x = VIEWPORT_SCALE_X (*x, w, viewport[2], viewport[0]);
*y = VIEWPORT_SCALE_Y (*y, w, viewport[3], viewport[1]);
*x = VIEWPORT_TRANSFORM_X (*x, viewport[0], viewport[2]);
*y = VIEWPORT_TRANSFORM_Y (*y, viewport[1], viewport[3]);
}
#undef VIEWPORT_SCALE_X