How do I implement two translations and a scale operation in GLSL?

问题

I am trying to implement the following transformation.

My original world-space coordinates are (2D) x=1586266800 and y=11812

I want:

the bottom left corner of the OpenGL image to represent coordinates (1586266800, 11800)
the top right corner of the OpenGL image to represent coordinates (1586267400, 11900)

In order to do that I plan to join three transformation matrices:

Translate to the origin of coordinates x=1586266800 and y=11800
Scale to have a width of 600 and a height of 100
Translate again -1.0f and -1.0f so the center of the OpenGL is at the bottom left.

I use the following transformation matrices:

Translation Matrix:

| 1 0 0 tx |
| 0 1 0 ty |
| 0 0 1 tz |
| 0 0 0 1  |

Scale Matrix:

| sx  0  0  0 |
|  0 sy  0  0 |
|  0  0 sz  0 |
|  0  0  0  1 |

In Octave I can implement the transformation as follows, multiplying three matrices:

>> candle
candle =
  1586266800
       11812
           0
           1
>> translation1
translation1 =
    1   0   0   -1586266800
    0   1   0        -11800
    0   0   1             0
    0   0   0             1

>> scale
scale =
   0.00333333333333333      0   0   0
                     0   0.02   0   0
                     0      0   1   0
                     0      0   0   1

(where `0.0033333 = 2/600` and `0.02 = 2/100`)

>> translation2
translation2 =
    1   0   0   -1
    0   1   0   -1
    0   0   1    0
    0   0   0    1

>> translation2*scale*translation1*candle
ans =

                    -1
    -0.759999999999991
                     0
                     1

Which translates the point to the right place in a -1.0f,1.0f OpenGL screen.

Now I am trying to replicate that in my Geometry shader, which receives the original world-space coordinates from the vertex shader.

I tried this:

#version 330 core

layout (points) in;
layout (line_strip, max_vertices = 12) out;

in uint gs_in_y[];
in uint gs_in_x[];

uniform uint xOrigin;
uniform uint xScaleWidth;
uniform uint yOrigin;
uniform uint yScaleWidth;

void main()
{

    // TRANSLATION MATRIX
    // [ 1 0 0 tx ]
    // [ 0 1 0 ty ]
    // [ 0 0 1 tz ]
    // [ 0 0 0 1  ]
    // mat3 m = mat3(
    //  1.1, 2.1, 3.1, // first column (not row!)
    //  1.2, 2.2, 3.2, // second column
    //  1.3, 2.3, 3.3  // third column
    //  );
    mat4 translation = mat4(
        1.0f, 0, 0, -xOrigin,
        0, 1.0f, 0, -yOrigin,
        0, 0, 1.0f, 0,
        0, 0, 0, 1.0f
    );


    // SCALE MATRIX
    // [ sx  0  0  0 ]
    // [  0 sy  0  0 ]
    // [  0  0 sz  0 ]
    // [  0  0  0  1 ]
    mat4 scale = mat4(
        2.0/xScaleWidth, 0, 0, 0,
        0, 2.0f/yScaleWidth, 0, 0,
         0,  0, 1.0f,  0,
         0,  0,  0,  1.0f
    );

    // FINAL TRANSLATION
    mat4 translationGl = mat4(
        1.0f,      0,    0,   -1.0f,
           0,   1.0f,    0,   -1.0f,
           0,      0, 1.0f,   0,
           0,      0,    0,   1.0f
    );

    gl_Position = translationGl * scale * translation * vec4(gs_in_x[0], gs_in_y[0], 0.0, 1.0);
    EmitVertex();    
    gl_Position = translationGl * scale * translation * vec4(gs_in_x[0]+30, gs_in_y[0], 0.0, 1.0); 
    EmitVertex();    
    EndPrimitive();

}

来源：https://stackoverflow.com/questions/61138427/how-do-i-implement-two-translations-and-a-scale-operation-in-glsl

标签

opengl

graphics

glsl