diff -r 4cbd9c0beb4c -r dc3c102e1264 OHP3D.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/OHP3D.cpp	Wed Dec 27 01:50:38 2023 +0100
@@ -0,0 +1,694 @@
+/**
+ * OHP3D
+ * Copyright © 2023 František Kučera (Frantovo.cz, GlobalCode.info)
+ *
+ * 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, version 3 of the License.
+ *
+ * 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 <iostream>
+#include <iomanip>
+#include <string>
+#include <charconv>
+#include <memory>
+#include <functional>
+#include <sstream>
+#include <vector>
+
+#include "x11.h"
+#include "opengl.h"
+#include "EPoll.h"
+#include "Logger.h"
+#include "MappedFile.h"
+#include "ImageLoader.h"
+#include "Texture.h"
+#include "Shader.h"
+#include "Program.h"
+#include "FileMonitor.h"
+#include "XAttrs.h"
+
+#include "OHP3D.h"
+
+class OHP3D::Impl {
+public:
+
+	struct {
+		GLint aVertexXYZ = -2;
+		GLint aTextureXY = -2;
+
+		GLint fColor = -2;
+
+		GLint uModel = -2;
+		GLint uView = -2;
+		GLint uProjection = -2;
+		GLint uTexture = -2;
+		GLint uTextureScale = -2;
+	} ProgAttr;
+
+	struct {
+		float yaw = -90.f;
+		float pitch = 0.f;
+		float roll = 0.f;
+		float fov = 45.0f;
+		glm::vec3 cameraPos = glm::vec3(0.0f, 0.0f, 3.0f);
+		glm::vec3 cameraFront = glm::vec3(0.0f, 0.0f, -1.0f);
+		glm::vec3 cameraUp = glm::vec3(0.0f, 1.0f, 0.0f);
+
+		void adjustFov(float diff) {
+			fov += diff;
+			if (fov < 1.0f) fov = 1.0f;
+			else if (fov > 120.0f) fov = 120.0f;
+			std::cerr << "field of view: " << fov << " °" << std::endl;
+		}
+
+		void moveForward(const float cameraSpeed) {
+			cameraPos += cameraSpeed * cameraFront;
+		}
+
+		void moveBackward(const float cameraSpeed) {
+			cameraPos -= cameraSpeed * cameraFront;
+		}
+
+		void moveLeft(const float cameraSpeed) {
+			cameraPos -= glm::normalize(
+					glm::cross(cameraFront, cameraUp)) * cameraSpeed;
+		}
+
+		void moveRight(const float cameraSpeed) {
+			cameraPos += glm::normalize(
+					glm::cross(cameraFront, cameraUp)) * cameraSpeed;
+		}
+
+		void moveUp(const float cameraSpeed) {
+			cameraPos += cameraSpeed * glm::normalize(cameraUp);
+		}
+
+		void moveDown(const float cameraSpeed) {
+			cameraPos -= cameraSpeed * glm::normalize(cameraUp);
+		}
+
+		void updateCameraFrontAndUp() {
+			std::cerr << "--- updateCameraFrontAndUp() --------" << std::endl;
+			dump("pitch, yaw, roll", glm::vec3(pitch, yaw, roll));
+			dump("cameraPos", cameraPos);
+			dump("cameraFront", cameraFront);
+			const auto pitchR = glm::radians(pitch); // around X axis
+			const auto yawR = glm::radians(yaw); //     around Y axis
+			const auto rollR = glm::radians(roll); //   around Z axis
+
+			cameraFront.x = cos(pitchR) * cos(yawR);
+			cameraFront.y = sin(pitchR);
+			cameraFront.z = cos(pitchR) * sin(yawR);
+			cameraFront = glm::normalize(cameraFront);
+			dump("cameraFront", cameraFront);
+			dump("cameraUp", cameraUp);
+
+			// TODO: review ROLL rotation and default angle
+			glm::mat4 rollMatrix = glm::rotate(
+					glm::mat4(1.0f), rollR, cameraFront);
+			cameraUp = glm::mat3(rollMatrix) * glm::vec3(0., 1., 0.);
+			dump("cameraUp", cameraUp);
+			std::cerr << "-------------------------------------" << std::endl;
+		}
+
+		void limitPitch() {
+			if (pitch > +89.0f) pitch = +89.0f;
+			if (pitch < -89.0f) pitch = -89.0f;
+		}
+
+		void turnLeft(const float angleSpeed) {
+			yaw -= angleSpeed;
+			updateCameraFrontAndUp();
+		}
+
+		void turnRight(const float angleSpeed) {
+			yaw += angleSpeed;
+			updateCameraFrontAndUp();
+		}
+
+		void turnUp(const float angleSpeed) {
+			pitch += angleSpeed;
+			limitPitch();
+			updateCameraFrontAndUp();
+		}
+
+		void turnDown(const float angleSpeed) {
+			pitch -= angleSpeed;
+			limitPitch();
+			updateCameraFrontAndUp();
+		}
+
+		void rollLeft(const float angleSpeed) {
+			roll += angleSpeed;
+			updateCameraFrontAndUp();
+		}
+
+		void rollRight(const float angleSpeed) {
+			roll -= angleSpeed;
+			updateCameraFrontAndUp();
+		}
+
+	} initialCtx, ctx;
+
+	Display* dpy;
+	Window win;
+	XVisualInfo* vi;
+	GLXContext glc;
+
+	FileMonitor fileMonitor;
+	std::vector<WatchedFile> watchedFiles;
+	ImageLoader imageLoader;
+	std::vector<std::shared_ptr<Shader>> shaders;
+	std::shared_ptr<Program> shaderProgram;
+	std::vector<std::shared_ptr<Texture>> textures;
+
+	Configuration cfg;
+	std::ostream& logOutput = std::cerr;
+
+	Impl(Configuration cfg) : cfg(cfg) {
+	}
+
+	void run();
+	void clear();
+	void runShaders();
+	Window getRootWindow(Window defaultValue);
+	void log(LogLevel level, std::string message);
+	int setNonBlocking(int fd);
+	void loadVertices();
+	void parametrizeTexture(std::shared_ptr<Texture> tex);
+	bool reloadTexture(const std::string& fileName);
+	void loadTextures();
+	void loadShaders();
+	void updateVariableLocations();
+	bool reloadShader(const std::string& fileName);
+	void setTitle(const std::string& suffix = "");
+	static const std::string getDefaultFile(const std::string& relativePath);
+
+};
+
+OHP3D::OHP3D(const Configuration& configuration) :
+impl(new Impl(configuration)) {
+}
+
+OHP3D::~OHP3D() {
+	impl->textures.clear();
+	impl->shaders.clear();
+	impl->shaderProgram = nullptr;
+	XFree(impl->vi);
+	glXMakeCurrent(impl->dpy, None, NULL);
+	glXDestroyContext(impl->dpy, impl->glc);
+	XDestroyWindow(impl->dpy, impl->win);
+	XCloseDisplay(impl->dpy);
+	delete impl;
+	// std::cerr << "~OHP3D()" << std::endl;
+}
+
+void OHP3D::Impl::setTitle(const std::string& suffix) {
+	std::stringstream title;
+	title << "OHP3D";
+	if (suffix.size()) title << ": " << suffix.c_str();
+	XStoreName(dpy, win, title.str().c_str());
+	XFlush(dpy);
+}
+
+void OHP3D::run() {
+	impl->run();
+}
+
+void OHP3D::Impl::run() {
+	dpy = XOpenDisplay(NULL);
+
+	if (dpy == NULL) throw std::logic_error("Unable to connect to X server");
+
+	GLint att[] = {GLX_RGBA, GLX_DEPTH_SIZE, 24, GLX_DOUBLEBUFFER, None};
+	vi = glXChooseVisual(dpy, 0, att);
+	Window root = DefaultRootWindow(dpy);
+	Window parent = cfg.rootWindow ? cfg.rootWindow : root;
+
+	XSetWindowAttributes swa;
+	swa.colormap = XCreateColormap(dpy, parent, vi->visual, AllocNone);
+	swa.event_mask = ExposureMask | KeyPressMask | PointerMotionMask
+			| ButtonPressMask
+			| StructureNotifyMask;
+
+	bool full = false;
+	unsigned int width = 1600;
+	unsigned int height = 1200;
+	if (parent != root) {
+		XWindowAttributes parentAttr;
+		XGetWindowAttributes(dpy, parent, &parentAttr);
+		width = parentAttr.width;
+		height = parentAttr.height;
+	}
+
+	win = XCreateWindow(
+			dpy, parent, 0, 0, width, height, 0,
+			vi->depth, InputOutput, vi->visual,
+			CWColormap | CWEventMask, &swa);
+
+	XMapWindow(dpy, win);
+	setTitle();
+	setX11PID(dpy, win);
+	// XSetWindowBackground(dpy, win, 0) vs. glClearColor()
+
+	glc = glXCreateContext(dpy, vi, NULL, GL_TRUE);
+	glXMakeCurrent(dpy, win, glc);
+
+	glEnable(GL_DEPTH_TEST);
+	glEnable(GL_BLEND);
+	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+
+	clear();
+	glXSwapBuffers(dpy, win);
+
+
+	// Load GLSL shaders:
+	loadShaders();
+	loadTextures();
+	loadVertices();
+
+	auto toggleFullscreen = [&]() {
+		full = setFullscreen(dpy, win, !full);
+	};
+
+	auto resetView = [&]() {
+		ctx = initialCtx;
+		ctx.updateCameraFrontAndUp();
+	};
+
+	// root can reize our window
+	// or we can listen to root resize and then resize our window ourselves
+	bool listenToRootResizes = true;
+	if (listenToRootResizes) XSelectInput(dpy, parent, StructureNotifyMask);
+
+	bool keepRunningX11 = true;
+	int x11fd = XConnectionNumber(dpy);
+	EPoll epoll;
+	epoll.add(x11fd);
+	epoll.add(fileMonitor.getFD());
+	try {
+		epoll.add(setNonBlocking(STDIN_FILENO));
+	} catch (const EPoll::Exception& e) {
+		logOutput << "Will not monitor events on STDIN: " << e.what() << "\n";
+	}
+
+	// rended the 3D scene even before the first event:
+	runShaders();
+	glXSwapBuffers(dpy, win);
+
+	for (XEvent xev; keepRunningX11;) {
+		int epollEventCount = epoll.wait();
+		//std::cout << "trace: epoll.wait() = " << epollEventCount << std::endl;
+		for (int epollEvent = 0; epollEvent < epollEventCount; epollEvent++) {
+			bool redraw = false;
+			if (epoll[epollEvent].data.fd == x11fd) {
+				if (!XPending(dpy)) {
+					// otherwise STDIN events are held until the first X11 event
+					logOutput << "trace: no pending X11 event" << std::endl;
+					break;
+				}
+process_x11_event:
+				XWindowAttributes gwa;
+				XNextEvent(dpy, &xev);
+
+				if (xev.type == Expose) {
+					std::cout << "XEvent: Expose" << std::endl;
+					XGetWindowAttributes(dpy, win, &gwa);
+					glViewport(0, 0, gwa.width, gwa.height);
+					redraw = true;
+				} else if (xev.type == KeyPress) {
+					DecodedKey key = decodeKeycode(dpy, xev.xkey.keycode);
+					std::cout << "XEvent: KeyPress:"
+							<< " keycode=" << key.code
+							<< " key=" << key.name
+							<< std::endl;
+
+					const float cSp = 0.05f; // camera speed
+					const float aSp = 5.f; // angle speed
+
+					if (key.matches(XK_q, XK_Escape)) keepRunningX11 = false;
+					else if (key.matches(XK_Left, XK_s)) ctx.turnLeft(aSp);
+					else if (key.matches(XK_Right, XK_f)) ctx.turnRight(aSp);
+					else if (key.matches(XK_Up, XK_e)) ctx.moveForward(cSp);
+					else if (key.matches(XK_Down, XK_d)) ctx.moveBackward(cSp);
+					else if (key.matches(XK_w)) ctx.rollLeft(aSp);
+					else if (key.matches(XK_r)) ctx.rollRight(aSp);
+					else if (key.matches(XK_t)) ctx.turnUp(aSp);
+					else if (key.matches(XK_g)) ctx.turnDown(aSp);
+					else if (key.matches(XK_m)) ctx.moveLeft(cSp);
+					else if (key.matches(XK_comma)) ctx.moveRight(cSp);
+					else if (key.matches(XK_l)) ctx.moveUp(cSp);
+					else if (key.matches(XK_period)) ctx.moveDown(cSp);
+					else if (key.matches(XK_j)) ctx.moveLeft(cSp * 5);
+					else if (key.matches(XK_k)) ctx.moveRight(cSp * 5);
+					else if (key.matches(XK_u)) ctx.moveLeft(cSp * 10);
+					else if (key.matches(XK_i)) ctx.moveRight(cSp * 10);
+					else if (key.matches(XK_x)) resetView();
+					else if (key.matches(XK_F11, XK_y)) toggleFullscreen();
+					redraw = true;
+				} else if (xev.type == ButtonPress) {
+					std::cout << "XEvent: ButtonPress:"
+							<< " button=" << xev.xbutton.button
+							<< std::endl;
+					if (xev.xbutton.button == 1);
+					else if (xev.xbutton.button == 4) ctx.adjustFov(-1.0);
+					else if (xev.xbutton.button == 5) ctx.adjustFov(+1.0);
+					else if (xev.xbutton.button == 8) resetView();
+					else if (xev.xbutton.button == 9) keepRunningX11 = false;
+					redraw = true;
+				} else if (xev.type == MotionNotify) {
+					// printCursorInfo(xev.xmotion);
+				} else if (xev.type == ConfigureNotify) {
+					std::cout << "XEvent: ConfigureNotify:"
+							<< " window=" << xev.xconfigure.window
+							<< " height=" << xev.xconfigure.height
+							<< " width=" << xev.xconfigure.width
+							<< std::endl;
+					if (listenToRootResizes
+							&& xev.xconfigure.window == parent) {
+						XResizeWindow(dpy, win,
+								xev.xconfigure.width, xev.xconfigure.height);
+					}
+				} else if (xev.type == UnmapNotify) {
+					std::cout << "XEvent: UnmapNotify" << std::endl;
+				} else if (xev.type == DestroyNotify) {
+					std::cout << "XEvent: DestroyNotify → finish" << std::endl;
+					break;
+				} else {
+					std::cout << "XEvent: type=" << xev.type << std::endl;
+				}
+				if (XPending(dpy)) goto process_x11_event;
+			} else if (epoll[epollEvent].data.fd == STDIN_FILENO) {
+				int epollFD = epoll[epollEvent].data.fd;
+				logOutput << "other event: fd=" << epollFD << " data=";
+				for (char ch; read(epollFD, &ch, 1) > 0;) {
+					std::stringstream msg;
+					msg
+							<< std::hex
+							<< std::setfill('0')
+							<< std::setw(2)
+							<< (int) ch;
+					logOutput << msg.str();
+				}
+				logOutput << std::endl;
+
+			} else if (epoll[epollEvent].data.fd == fileMonitor.getFD()) {
+				std::cout << "FileMonitor event:" << std::endl;
+				for (FileEvent fe; fileMonitor.readEvent(fe);) {
+					logOutput << "   "
+							<< " file=" << fe.fileName
+							<< " mask=" << fe.mask
+							<< std::endl;
+					try {
+						redraw |= reloadTexture(fe.fileName);
+						redraw |= reloadShader(fe.fileName);
+						setTitle();
+					} catch (const std::exception& e) {
+						setTitle("[ERROR]");
+						logOutput << "error while reloading '"
+								<< fe.fileName.c_str()
+								<< "': " << e.what() << std::endl;
+					}
+				}
+			} else {
+				logOutput
+						<< "error: event on an unexpected FD: "
+						<< epoll[epollEvent].data.fd
+						<< std::endl;
+			}
+
+			if (redraw) {
+				runShaders();
+				glXSwapBuffers(dpy, win);
+			}
+		}
+	}
+}
+
+void OHP3D::Impl::clear() {
+	glClearColor(
+			(cfg.backgroundColor >> 16 & 0xFF) / 256.,
+			(cfg.backgroundColor >> 8 & 0xFF) / 256.,
+			(cfg.backgroundColor & 0xFF) / 256.,
+			1.0);
+	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+}
+
+void OHP3D::Impl::runShaders() {
+	shaderProgram->use();
+	checkError(&std::cerr);
+
+	clear();
+
+	GLint viewport[4];
+	glGetIntegerv(GL_VIEWPORT, viewport);
+	GLfloat width = viewport[2];
+	GLfloat height = viewport[3];
+
+	glm::mat4 projection = glm::perspective(
+			glm::radians(ctx.fov),
+			width / height,
+			0.1f, 100.0f);
+	glUniformMatrix4fv(ProgAttr.uProjection, 1, GL_FALSE, &projection[0][0]);
+
+	glm::mat4 view = glm::lookAt(
+			ctx.cameraPos,
+			ctx.cameraPos + ctx.cameraFront,
+			ctx.cameraUp);
+	glUniformMatrix4fv(ProgAttr.uView, 1, GL_FALSE, &view[0][0]);
+
+	// glBindVertexArray(vao);
+
+	glm::mat4 model = glm::mat4(1.0f); // identity matrix
+	glUniformMatrix4fv(ProgAttr.uModel, 1, GL_FALSE, &model[0][0]);
+
+	// TODO: draw a rectangle for each texture
+	glUniform1f(ProgAttr.uTextureScale, textures[0]->getScale());
+
+	glDrawArrays(GL_TRIANGLES, 0, 2 * 3); // see loadVertices()
+	std::cerr << "GLSL: glDrawArrays()" << std::endl;
+}
+
+void OHP3D::Impl::log(LogLevel level, std::string message) {
+	::log(logOutput, level, message);
+}
+
+int OHP3D::Impl::setNonBlocking(int fd) {
+	int flags = fcntl(fd, F_GETFL, 0);
+	fcntl(fd, F_SETFL, flags | O_NONBLOCK);
+	return fd;
+}
+
+void OHP3D::Impl::loadVertices() {
+	for (int i = 0; i < textures.size(); i++) {
+		std::shared_ptr<Texture> tex = textures[i];
+		// TODO: draw a rectangle for each texture
+		GLfloat ratio = tex->getRatio();
+		const std::vector<GLfloat> vertices = {
+			// Vertex XYZ                      Texture XY
+			-0.80f * ratio, +0.80f, +0.0, /**/ 0.0, 0.0,
+			+0.80f * ratio, +0.80f, +0.0, /**/ 1.0, 0.0,
+			-0.80f * ratio, -0.80f, +0.0, /**/ 0.0, 1.0,
+
+			-0.80f * ratio, -0.80f, +0.0, /**/ 0.0, 1.0,
+			+0.80f * ratio, -0.80f, +0.0, /**/ 1.0, 1.0,
+			+0.80f * ratio, +0.80f, +0.0, /**/ 1.0, 0.0,
+
+			// see glDrawArrays(), where we set start offset and count
+		};
+
+		// Vertex data:
+		glVertexAttribPointer(ProgAttr.aVertexXYZ, 3, // vertex items
+				GL_FLOAT, GL_FALSE, 5 * sizeof (float),
+				(void*) 0);
+		glEnableVertexAttribArray(ProgAttr.aVertexXYZ);
+
+		// Texture positions:
+		glVertexAttribPointer(ProgAttr.aTextureXY, 2, // texture items
+				GL_FLOAT, GL_FALSE, 5 * sizeof (float),
+				(void*) (3 * sizeof (float)));
+		glEnableVertexAttribArray(ProgAttr.aTextureXY);
+
+		glBufferData(GL_ARRAY_BUFFER,
+				vertices.size() * sizeof (vertices[0]),
+				vertices.data(),
+				GL_STATIC_DRAW);
+		// GL_STATIC_DRAW:
+		//   The vertex data will be uploaded once
+		//   and drawn many times(e.g. the world).
+		// GL_DYNAMIC_DRAW:
+		//   The vertex data will be created once, changed from
+		// 	 time to time, but drawn many times more than that.
+		// GL_STREAM_DRAW:
+		//   The vertex data will be uploaded once and drawn once.
+
+		// see also glBindBuffer(GL_ARRAY_BUFFER, vbo); where we set current VBO
+	}
+}
+
+const std::string
+OHP3D::Impl::getDefaultFile(const std::string& relativePath) {
+	const char* envName = "OHP3D_DATA_DIR";
+	const char* envValue = ::getenv(envName);
+	if (envValue) {
+		return std::string(envValue) + "/" + relativePath;
+	} else {
+		throw std::invalid_argument(std::string("Configure $") + envName
+				+ " in order to use defaults"
+				" or specify textures and shaders as parameters");
+	}
+}
+
+void OHP3D::Impl::parametrizeTexture(std::shared_ptr<Texture> tex) {
+	XAttrs xa(tex->getFileName());
+	std::string magf = xa["ohp3d.texture.mag-filter"];
+	std::string minf = xa["ohp3d.texture.min-filter"];
+	std::string scale = xa["ohp3d.texture.scale"];
+
+	auto GLT2D = GL_TEXTURE_2D;
+	auto MAG = GL_TEXTURE_MAG_FILTER;
+	auto MIN = GL_TEXTURE_MIN_FILTER;
+
+	if (magf == "linear") glTexParameteri(GLT2D, MAG, GL_LINEAR);
+	else if (magf == "nearest") glTexParameteri(GLT2D, MAG, GL_NEAREST);
+
+	if (minf == "linear") glTexParameteri(GLT2D, MIN, GL_LINEAR);
+	else if (minf == "nearest") glTexParameteri(GLT2D, MIN, GL_NEAREST);
+
+	if (scale.size()) {
+		float sc;
+		if (std::from_chars(scale.data(), scale.data() + scale.size(), sc).ec
+				== std::errc{}) tex->setScale(sc);
+		else std::cerr << "Invalid texture scale value - expecting float\n";
+		// tex->setScale(std::stof(scale)); // locale-dependent (. vs ,)
+	}
+}
+
+void OHP3D::Impl::loadTextures() {
+	// Load default texture if there is no configured:
+	if (cfg.textures.empty())
+		cfg.textures.push_back({getDefaultFile("textures/default.png")});
+
+	for (const Configuration::Texture& tex : cfg.textures) {
+		std::shared_ptr<ImageLoader::ImageBuffer>
+				img(imageLoader.loadImage(MappedFile(tex.fileName)));
+		textures.push_back(std::make_shared<Texture>(
+				img->width, img->height, *img, tex.fileName));
+		parametrizeTexture(textures.back());
+		// static const uint32_t watchMask = IN_CLOSE_WRITE | IN_ATTRIB;
+		// watchedFiles.push_back(fileMonitor.watch(tex.fileName, watchMask));
+		watchedFiles.push_back(fileMonitor.watch(tex.fileName));
+		// TODO: review texture loading and binding
+		// works even without this - default texture
+		// glUniform1i(..., ...);
+		// checkError(&std::cerr);
+	}
+}
+
+bool OHP3D::Impl::reloadTexture(const std::string& fileName) {
+	for (std::shared_ptr<Texture> tex : textures) {
+		if (tex->getFileName() == fileName) {
+			std::shared_ptr<ImageLoader::ImageBuffer>
+					img(imageLoader.loadImage(MappedFile(fileName)));
+			tex->update(img->width, img->height, *img);
+			parametrizeTexture(tex);
+			loadVertices();
+			return true;
+		}
+	}
+	return false;
+}
+
+void OHP3D::Impl::loadShaders() {
+	// Vertex Array Object (VAO)
+	GLuint vao;
+	glGenVertexArrays(1, &vao);
+	glBindVertexArray(vao);
+	// VAO - something like context for bound data/variables
+	// We can switch multiple VAOs. VAO can contain multiple VBOs.
+	// what-are-vertex-array-objects
+
+	// Vertex Buffer Object (VBO):
+	GLuint vbo;
+	glGenBuffers(1, &vbo);
+	glBindBuffer(GL_ARRAY_BUFFER, vbo);
+
+	{
+		// Load default shaders if there are no configured:
+		int vc = 0;
+		int fc = 0;
+		auto& ss = cfg.shaders;
+		for (const auto& s : ss) if (s.type == "vertex") vc++;
+		for (const auto& s : ss) if (s.type == "fragment") fc++;
+		auto& d = getDefaultFile;
+		if (vc == 0) ss.push_back({d("shaders/default.vert"), "vertex"});
+		if (fc == 0) ss.push_back({d("shaders/default.frag"), "fragment"});
+	}
+
+	shaderProgram = std::make_shared<Program>();
+
+	// glBindFragDataLocation(program, 0, "outColor");
+	// glBindAttribLocation(program, LOC.input, "vertices");
+
+	for (const Configuration::Shader definition : cfg.shaders) {
+		Shader::Type type;
+		std::string fileName = definition.fileName;
+		if (definition.type == "fragment") type = Shader::Type::FRAGMENT;
+		else if (definition.type == "vertex") type = Shader::Type::VERTEX;
+		else throw std::invalid_argument("unsupported shader type");
+
+		MappedFile file(fileName);
+		std::shared_ptr<Shader> shader = std::make_shared<Shader>(
+				type, file, fileName);
+
+		shaderProgram->attachShader(*shader.get());
+		shaders.push_back(shader);
+		watchedFiles.push_back(fileMonitor.watch(fileName));
+		std::cerr << "GLSL loaded: " << fileName.c_str() << std::endl;
+		// We may detach and delete shaders,
+		// but our shaders are small, so we keep them for later reloading.
+	}
+
+	shaderProgram->link();
+	updateVariableLocations();
+	// listVariables(program);
+	std::cerr << "GLSL shader count: " << shaders.size() << std::endl;
+}
+
+void OHP3D::Impl::updateVariableLocations() {
+	// GLSL compiler does very efficient / aggressive optimization.
+	// Attributes and uniforms that are not used in the shader are deleted.
+	// And even if we e.g. read color from a texture and overwrite it,
+	// the variable is still deleted and considered „inactive“.
+	// Functions glGetAttribLocation() and glGetUniformLocation() return -1.
+	ProgAttr.aVertexXYZ = shaderProgram->getAttribLocation("aVertexXYZ");
+	ProgAttr.aTextureXY = shaderProgram->getAttribLocation("aTextureXY");
+	ProgAttr.uModel = shaderProgram->getUniformLocation("uModel");
+	ProgAttr.uView = shaderProgram->getUniformLocation("uView");
+	ProgAttr.uProjection = shaderProgram->getUniformLocation("uProjection");
+	ProgAttr.uTexture = shaderProgram->getUniformLocation("uTexture");
+	ProgAttr.uTextureScale = shaderProgram->getUniformLocation("uTextureScale");
+	ProgAttr.fColor = shaderProgram->getFragDataLocation("fColor");
+	shaderProgram->bindFragDataLocation("fColor", ProgAttr.fColor);
+}
+
+bool OHP3D::Impl::reloadShader(const std::string& fileName) {
+	for (auto shader : shaders) {
+		if (shader->getFileName() == fileName) {
+			shader->update(MappedFile(fileName));
+			shaderProgram->link();
+			updateVariableLocations();
+			return true;
+		}
+	}
+	return false;
+}