GACCUM_TRAN_MATRIX(3NCARG)

💅 GACCUM_TRAN_MATRIX 💅

okay bestie, welcome to a page straight out of NCAR GRAPHICS ✨ and yes, the manual name is literally NCAR Graphics, we're doing vintage graphics programming today and it's giving main character energy fr fr.

This one's about gaccum_tran_matrix, aka Accumulate transformation matrix — and no cap, it's the one you call when you want to build a GKS segment transformation matrix by starting with a matrix you already have and composing it with a shift vector, a rotation angle, and X and Y scale factors, so you end up with a brand new transformation matrix 🦋. The rotation and the scaling? Both happen with respect to a user-defined fixed point. Iconic. Periodt.

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🌸 SYNOPSIS 🌸

#include <ncarg/gks.h>

void gaccum_tran_matrix(const Gtran_matrix t_matrix, const Gpoint
*point, const Gvec *shift, Gdouble angle, const Gvec *scale,
Gcoord_switch coord_switch, Gtran_matrix tran_matrix);

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💖 DESCRIPTION 💖

okay so here's the tea on every single argument, don't skip, they all matter 🫶

• t_matrix (Gfloat, Input) — a 2x3 GKS transformation matrix. This is your starting point, your base, your before-pic.
• point.x (Gfloat, Input) — the X coordinate value for a fixed point that gets used for the scaling and rotation parts of the output transformation. And here's the thing: point.x is either in world coordinates or normalized device coordinates depending on how the argument coord_switch is set (more on that below, we'll get there 💅).
• point.y (Gfloat, Input) — the Y coordinate value for that same fixed point, used for the scaling and rotation parts of the output transformation. Same deal as point.x: it's either in world coordinates or normalized device coordinates depending on how coord_switch is set.
• shift.delta_x (Gfloat, Input) — the X component of a shift vector, used for the scaling part of the output transformation. And yep, shift.delta_x is either in world coordinates or normalized device coordinates depending on the setting of coord_switch described below.
• shift.delta_y (Gfloat, Input) — the Y component of that shift vector, used for the scaling part of the output transformation. Also either in world coordinates or normalized device coordinates depending on coord_switch.
• angle (Input) — the rotation angle, in radians, used for the rotation part of the output transformation. Radians bestie, not degrees, we don't do degrees here 😭
• scale.delta_x (Gfloat, Input) — the X coordinate scale factor used in the scaling part of the output transformation.
• scale.delta_y (Gfloat, Input) — the Y coordinate scale factor used in the scaling part of the output transformation.
• coord_switch (Input) — a coordinate switch that tells the routine whether the values for the arguments point and shift (both described above, keep up 💖) are in world coordinates or normalized device coordinates. The possible values include:
  • GCOORD_WC — World coordinates
  • GCOORD_NDC — Normalized device coordinates
• tran_matrix (Gfloat, Output) — a 2x3 array that holds the GKS transformation matrix in a form you can feed straight into other GKS functions, like gset_seg_tran. This matrix gets constructed by composing the scale, rotate, and shift input (all described above) with the original input matrix t_matrix. Slay.

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🦋 USAGE 🦋

so if you're using world coordinates, the shift vector and the fixed point get transformed by the current normalization transformation. Just how it is ✨

The order in which the transformations are applied is: input matrix, scale, rotate, and shift. That order. In that sequence. Don't come for me, that's the order 💅

Elements tran_matrix[0][2] and tran_matrix[1][2] are in normalized device coordinates, and the other elements of tran_matrix are unitless. Noted, bestie 🎀

Also, gaccum_tran_matrix can be used to construct more general transformation matrices than geval_tran_matrix can. The most common usage of gaccum_tran_matrix is to change the order in which the operations of scale, rotate, and shift are applied — because that order is fixed in geval_tran_matrix, lowkey rigid of it. The example below shows how to construct a transformation matrix that shifts first and then rotates. Obsessed with the flexibility honestly 🔥

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🎀 EXAMPLE 🎀

Assuming that the input matrix t_matrix is initially the identity, the following code

      pi = 3.1415926;
      point.x = point.y = 0.5;
      shift.delta_x = 0.25;
      shift.delta_y = 0.;
      scale.delta_x = 1.0;
      scale.delta_y = 1.0;
      gaccum_tran_matrix(t_matrix,&point,&shift,0.,&scale,GCOORD_WC,tout);
      for( i = 0; i < 2; i++ ) {
          for( j = 0; j < 3; j++ ) {
              t_matrix[i][j] = tout[i][j];
          }
      }
      shift.delta_x = 0.;
      shift.delta_y = 0.;
      gaccum_tran_matrix(t_matrix,&point,&shift,45.*pi/180.,&scale,GCOORD_WC,tout);

would produce a transformation matrix in tout that would shift by (.25,0.) first, and then rotate by 45 degrees. Two steps, one matrix, chef's kiss 💜

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🔥 ACCESS 🔥

To use the GKS C-binding routines, load the ncarg_gks and ncarg_c libraries. That's the whole vibe check ✅

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💜 SEE ALSO 💜

Online: geval_tran_matrix(3NCARG), gclose_seg(3NCARG), gcreate_seg(3NCARG), gcopy_seg_ws(3NCARG), gdel_seg(3NCARG), ginq_name_open_seg(3NCARG), ginq_set_seg_names(3NCARG), gset_seg_tran(3NCARG), gks(3NCARG), ncarg_gks_cbind(3NCARG)

Hardcopy: User's Guide for NCAR GKS-0A Graphics; NCAR Graphics Fundamentals, UNIX Version

iykyk, go read those next bestie 📚✨

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👑 COPYRIGHT 👑

Copyright (C) 1987-2009 University Corporation for Atmospheric Research The use of this Software is governed by a License Agreement.

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okay that's the whole page, you ate it, no crumbs left 💅✨ one last thing though — this was the UNIX version, dated March 1993, and the page goes by GACCUM_TRAN_MATRIX(3NCARG). Byeee, go build something cute with your transformation matrices 🎀🦋💖