user
Using the triangle geometry from OpenGL. But instead of using a mechanism such as glColor3d, use a pixel shader for each pixel in the triangle. The pixel shader should pick a random RGB color for each pixel. Most pixels should have colors which are different from that of most other pixels.

Optional: provide an update mechanism, to repeatedly re-render the triangle. (Possibilities include a mouse event handler, a timer event handler or an infinite loop, or even window expose events.) Shader generated color for each pixel should be different in each render.

Optional: after updating the opengl rendering target but before rendering the triangle, query the opengl implementation to determine which versions of shaders are supported by the rendering target, list the tested shaders and the available shaders and then use a supported shader.

See also: opengl.org's gl shader language documentation, and lighthouse3d.com's glsl tutorial.
assistant
**Translation of**: C

```
# 20250207 Raku programming solution

use NativeCall;

my ($angle, $r_mod) = 0e0;

# OpenGL and GLUT constants
enum GLenum ( GL_TRIANGLES => 0x0004);

enum GLbitfield ( GL_COLOR_BUFFER_BIT => 0x00004000, GL_DEPTH_BUFFER_BIT => 0x00000100 );
enum GLUTdisplay_mode ( GLUT_RGB => 0x0000, GLUT_DOUBLE => 0x0002, GLUT_DEPTH => 0x0010 );
enum Shader_type ( GL_FRAGMENT_SHADER => 0x8B30, GL_VERTEX_SHADER => 0x8B31 );
enum STDLIB ( RAND_MAX => 2147483647 );

# GLUT functions
constant $lib = 'glut';
sub glutInit(CArray[uint32], CArray[Str]) is native($lib) {*}
sub glutInitDisplayMode(uint32 $mode) is native($lib) {*}
sub glutInitWindowSize(int32 $width, int32 $height) is native($lib) {*}
sub glutCreateWindow(Str $str) is native($lib) {*}
sub glutDisplayFunc(&func ()) is native($lib) {*}
sub glutIdleFunc(&func ()) is native($lib) {*}
sub glutSwapBuffers() is native($lib) {*}
sub glutMainLoop() is native($lib) {*}

# OpenGL functions
constant $gllib = 'GL';
sub glClear(int32) is native($gllib) {*}
sub glLoadIdentity() is native($gllib) {*}
sub glRotatef(num32 $angle, num32 $x, num32 $y, num32 $z) is native($gllib) {*}
sub glBegin(uint32) is native($gllib) {*}
sub glEnd() is native($gllib) {*}
sub glVertex3f(num32 $x, num32 $y, num32 $z) is native($gllib) {*}
sub glUniform1f(uint32, num32) is native($gllib) {*}

# Shader functions
sub glCreateShader(uint32) returns uint32 is native($gllib) {*}
sub glShaderSource(uint32, int32, CArray[Str], CArray[int32]) is native($gllib) {*}
sub glCompileShader(uint32) is native($gllib) {*}
sub glCreateProgram() returns uint32 is native($gllib) {*}
sub glAttachShader(uint32, uint32) is native($gllib) {*}
sub glLinkProgram(uint32) is native($gllib) {*}
sub glUseProgram(uint32) is native($gllib) {*}
sub glGetUniformLocation(uint32, Str) returns uint32 is native($gllib) {*}

# GLEW functions
constant $glewlib = 'GLEW';
sub glewInit() returns int32 is native($glewlib) {*}
sub glewIsSupported(Str) returns int32 is native($glewlib) {*}

sub render() {
   glClear(GL_COLOR_BUFFER_BIT +| GL_DEPTH_BUFFER_BIT);
   glUniform1f($r_mod, rand / RAND_MAX);
   glLoadIdentity();
   glRotatef($angle, $angle * 0.1, 1e0, 0e0);
   glBegin(GL_TRIANGLES);
      glVertex3f(-1e0, -0.5e0, 0e0);
      glVertex3f(0e0, 1e0, 0e0);
      glVertex3f(1e0, 0e0, 0e0);
   glEnd();
   $angle += 0.02;
   glutSwapBuffers();
}

sub compile_shader($shader_type, $source) {
   my $shader = glCreateShader($shader_type);
   my $length = $source.chars;
   my $source_array = CArray[Str].new($source);
   my $length_array = CArray[int32].new($length);
   glShaderSource($shader, 1, $source_array, $length_array);
   glCompileShader($shader);
   return $shader;
}

sub set_shader() {
   my $f = q:to/END/;
varying float x, y, z;
uniform float r_mod;
float rand(float s, float r) { return mod(mod(s, r + r_mod) * 112341.0, 1.0); }
void main() {
   gl_FragColor = vec4(rand(gl_FragCoord.x, x), rand(gl_FragCoord.y, y), rand(gl_FragCoord.z, z), 1.0);
}
END
   my $v = q:to/END/;
varying float x, y, z;
void main() {
   gl_Position = ftransform();
   x = gl_Position.x; y = gl_Position.y; z = gl_Position.z;
   x += y; y -= x; z += x - y;
}
END

   my $vs = compile_shader(GL_VERTEX_SHADER, $v);
   my $ps = compile_shader(GL_FRAGMENT_SHADER, $f);

   given my $prog = glCreateProgram() {
      ($vs, $ps).map: -> $shader { glAttachShader($prog, $shader) };
      glLinkProgram($prog);
      glUseProgram($prog);
      $r_mod = glGetUniformLocation($prog, "r_mod");
   }   
}

glutInit(CArray[uint32].new, CArray[Str].new);
glutInitDisplayMode(GLUT_DOUBLE +| GLUT_RGB +| GLUT_DEPTH);
glutInitWindowSize(600, 600);
glutCreateWindow("pixel shader");
glutDisplayFunc(&render);
glutIdleFunc(&render);
glewInit();
die "GL 2.0 unsupported\n" unless glewIsSupported("GL_VERSION_2_0"); 
set_shader();
glutMainLoop();

```