src/gl/gridprogram.cpp

/*
 *  LDForge: LDraw parts authoring CAD
 *  Copyright (C) 2020 Teemu Piippo
 *
 *  This program is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */

#include "gridprogram.h"

// Based on https://stackoverflow.com/q/30842755
const char vertexShaderSource[] = R"(
#version 330 core

layout (location = 0) in vec2 in_position;
uniform mat4 view;
uniform mat4 projection;
uniform mat4 model;
smooth out vec2 ex_uv;
const mat4 stretch = mat4(vec4(10000, 0, 0, 0), vec4(0, 10000, 0, 0), vec4(0, 0, 10000, 0), vec4(0, 0, 0, 1));
const mat4 gridmatrix = mat4(vec4(1, 0, 0, 0), vec4(0, 1, 0, 0), vec4(0, 0, 1, 0), vec4(0, 0, 0, 1));

void main()
{
	gl_Position = projection * view * model * gridmatrix * stretch * vec4(in_position, 0.0, 1.0);
	ex_uv = in_position;
}
)";

const char fragmentShaderSource[] = R"(
#version 330 core

out vec4 color;
smooth in vec2 ex_uv;
const vec4 lineColor = vec4(1.0, 1.0, 1.0, 0.75);
const float pi = 3.14159265f;

void main(void)
{
	float dx = fract(ex_uv.y / 0.0001f);
	float dy = fract(ex_uv.x / 0.0001f);
	/* compute distance to nearest unit line */
	float d = min(min(min(dy, dx), 1 - dy), 1 - dx);
	/* use an extreme sigmoid to bring out the grid shape */
	d = pow(1 - d, 50);
	/* fade the grid towards extreme co-ordinates */
	d = (1.0f - 20 * max(abs(ex_uv.x), abs(ex_uv.y))) * d;
	/* add dashes */
	d *= (1 + cos(ex_uv.y / 0.00001f * pi)) * 0.5f;
	d *= (1 + cos(ex_uv.x / 0.00001f * pi)) * 0.5f;
	color = vec4(lineColor.xyz, d);
}
)";

static const glm::vec2 data[] = {{-1, -1}, {-1, 1}, {1, 1}, {1, -1}};

GridProgram::GridProgram(QObject* parent) :
	QObject{parent},
	buffer{QOpenGLBuffer::VertexBuffer},
	vertexShader{QOpenGLShader::Vertex},
	fragmentShader{QOpenGLShader::Fragment}
{
}

void GridProgram::initialize()
{
	if (not isInitialized)
	{
		this->initializeOpenGLFunctions();
		this->isInitialized = true;
		this->program.emplace(this);
		gl::buildShaders(&*this->program, ::vertexShaderSource, ::fragmentShaderSource);
		this->program->bind();
		this->buffer.create();
		this->buffer.bind();
		this->buffer.setUsagePattern(QOpenGLBuffer::StaticDraw);
		this->buffer.allocate(data, countof(data) * sizeof data[0]);
		this->vertexArrayObject.create();
		this->vertexArrayObject.bind();
		this->program->enableAttributeArray(0);
		this->program->setAttributeBuffer(0, GL_FLOAT, 0, 2, 0);
		this->vertexArrayObject.release();
		this->buffer.release();
		this->program->release();
		this->checkForGLErrors();
	}
}

void GridProgram::setViewMatrix(const glm::mat4& newViewMatrix)
{
	Q_ASSERT(this->isInitialized);
	this->program->bind();
	this->program->setUniformMatrix("view", newViewMatrix);
	this->program->release();
	this->checkForGLErrors();
}

void GridProgram::setProjectionMatrix(const glm::mat4& newProjectionMatrix)
{
	Q_ASSERT(this->isInitialized);
	this->program->bind();
	this->program->setUniformMatrix("projection", newProjectionMatrix);
	this->program->release();
	this->checkForGLErrors();
}

void GridProgram::setModelMatrix(const glm::mat4& newModelMatrix)
{
	Q_ASSERT(this->isInitialized);
	this->program->bind();
	this->program->setUniformMatrix("model", newModelMatrix);
	this->program->release();
	this->checkForGLErrors();
}

void GridProgram::draw()
{
	this->program->bind();
	this->vertexArrayObject.bind();
	glDrawArrays(GL_QUADS, 0, countof(data));
	this->vertexArrayObject.release();
	this->program->release();
	this->checkForGLErrors();
}

void GridProgram::teardown()
{
	this->vertexArrayObject.destroy();
	this->buffer.destroy();
	this->program.reset();
}

void GridProgram::checkForGLErrors()
{
	gl::checkForGLErrors(qobject_cast<QWidget*>(this->parent()));
}