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101 lines
2.0 KiB
C
Executable File
101 lines
2.0 KiB
C
Executable File
#include "linmath.h"
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#include <math.h>
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#include <string.h>
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/* Adapted from Android's OpenGL Matrix.java. */
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static inline void mat4x4_perspective(mat4x4 m, float y_fov_in_degrees, float aspect, float n, float f)
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{
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const float angle_in_radians = (float) (y_fov_in_degrees * M_PI / 180.0);
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const float a = (float) (1.0 / tan(angle_in_radians / 2.0));
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m[0][0] = a / aspect;
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m[1][0] = 0.0f;
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m[2][0] = 0.0f;
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m[3][0] = 0.0f;
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m[1][0] = 0.0f;
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m[1][1] = a;
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m[1][2] = 0.0f;
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m[1][3] = 0.0f;
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m[2][0] = 0.0f;
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m[2][1] = 0.0f;
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m[2][2] = -((f + n) / (f - n));
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m[2][3] = -1.0f;
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m[3][0] = 0.0f;
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m[3][1] = 0.0f;
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m[3][2] = -((2.0f * f * n) / (f - n));
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m[3][3] = 0.0f;
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}
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static inline void mat4x4_translate_in_place(mat4x4 m, float x, float y, float z)
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{
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int i;
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for (i = 0; i < 4; ++i) {
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m[3][i] += m[0][i] * x
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+ m[1][i] * y
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+ m[2][i] * z;
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}
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}
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static inline void mat4x4_look_at(mat4x4 m,
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float eyeX, float eyeY, float eyeZ,
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float centerX, float centerY, float centerZ,
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float upX, float upY, float upZ)
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{
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// See the OpenGL GLUT documentation for gluLookAt for a description
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// of the algorithm. We implement it in a straightforward way:
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float fx = centerX - eyeX;
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float fy = centerY - eyeY;
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float fz = centerZ - eyeZ;
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// Normalize f
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vec3 f_vec = {fx, fy, fz};
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float rlf = 1.0f / vec3_len(f_vec);
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fx *= rlf;
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fy *= rlf;
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fz *= rlf;
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// compute s = f x up (x means "cross product")
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float sx = fy * upZ - fz * upY;
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float sy = fz * upX - fx * upZ;
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float sz = fx * upY - fy * upX;
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// and normalize s
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vec3 s_vec = {sx, sy, sz};
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float rls = 1.0f / vec3_len(s_vec);
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sx *= rls;
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sy *= rls;
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sz *= rls;
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// compute u = s x f
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float ux = sy * fz - sz * fy;
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float uy = sz * fx - sx * fz;
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float uz = sx * fy - sy * fx;
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m[0][0] = sx;
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m[0][1] = ux;
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m[0][2] = -fx;
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m[0][3] = 0.0f;
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m[1][0] = sy;
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m[1][1] = uy;
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m[1][2] = -fy;
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m[1][3] = 0.0f;
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m[2][0] = sz;
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m[2][1] = uz;
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m[2][2] = -fz;
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m[2][3] = 0.0f;
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m[3][0] = 0.0f;
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m[3][1] = 0.0f;
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m[3][2] = 0.0f;
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m[3][3] = 1.0f;
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mat4x4_translate_in_place(m, -eyeX, -eyeY, -eyeZ);
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}
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