File: shader-render

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#!/usr/bin/env perl
use strict;
use warnings;
use 5.010;

use OpenGL qw(:all);
use Math::Trig;
use Time::HiRes qw(sleep time);

####### GL HANDLERS
sub handler_resize {
	glViewport(0, 0, $_[0], $_[1]);
}

sub handler_idle {
	handler_render();

	glFlush();
	glutSwapBuffers();
	sleep(1 / 50);
}

sub init_gl {
	glutInit();
	glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGBA | GLUT_DEPTH);
	glutInitWindowSize(512, 512);
	glutCreateWindow("example");

	glutReshapeFunc   (\&handler_resize);
	glutIdleFunc      (\&handler_idle);
	glutDisplayFunc   (\&handler_render);
}

sub init_vp {
	glClearColor(0.0, 0.0, 0.0, 0.0);
	glColor3f(1.0, 1.0, 1.0);

	glMatrixMode(GL_PROJECTION);
	glOrtho(-1.0, 1.0, 1.0, -1.0, 1, -1);
	glMatrixMode(GL_TEXTURE);
	glMatrixMode(GL_MODELVIEW);

	glEnable(GL_TEXTURE_2D);
	# glEnable(GL_BLEND);
	# glBlendFunc(GL_SRC_ALPHA, GL_ONE);
}


init_gl();
init_vp();

# #########

sub handler_render {
	# ...
	glClear(GL_COLOR_BUFFER_BIT);
	glLoadIdentity();

	glPushMatrix();
	glBegin(GL_QUADS);
		glTexCoord2f(0, 0); glVertex2f(-1, -1);
		glTexCoord2f(0, 1); glVertex2f(-1,  1);
		glTexCoord2f(1, 1); glVertex2f( 1,  1);
		glTexCoord2f(1, 0); glVertex2f( 1, -1);
	glEnd();
	glPopMatrix();
}

my $fragment_id = glCreateShaderObjectARB(GL_FRAGMENT_SHADER_ARB);
glShaderSourceARB_p($fragment_id, << "__END_SHADER__");
void main() {
	float dist = length(gl_TexCoord[0].xy - 0.5);
	float val = sin(3.141 / (0.001 + 2 * dist)) / 2 + 0.5;
	gl_FragColor = vec4(val, val, val, 1.0);
}
__END_SHADER__
glCompileShaderARB($fragment_id);
my $stat = glGetInfoLogARB_p($fragment_id);
print "WARN shader compile $stat\n" if $stat;

my $shader_prog = glCreateProgramObjectARB();
glAttachObjectARB($shader_prog, $fragment_id);
glLinkProgramARB($shader_prog);

if (!glGetObjectParameterivARB_p($shader_prog, GL_OBJECT_LINK_STATUS_ARB)) {
	my $stat = glGetInfoLogARB_p($shader_prog);
	die("Failed to link shader program: $stat - dying");
}

glUseProgramObjectARB($shader_prog);

glutMainLoop();