From 1e08193a1678675ac5869b76e8a2339f6de5b773 Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Thu, 26 Feb 2026 18:04:06 +0000
Subject: Support for the BillboardPainter

Based on the ShadowStenciller, creates flattened images of a model for
simplified mass use in a scene.
---
 gfx/gl/billboardPainter.cpp | 92 +++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 92 insertions(+)
 create mode 100644 gfx/gl/billboardPainter.cpp

(limited to 'gfx/gl/billboardPainter.cpp')

diff --git a/gfx/gl/billboardPainter.cpp b/gfx/gl/billboardPainter.cpp
new file mode 100644
index 0000000..e72e72d
--- /dev/null
+++ b/gfx/gl/billboardPainter.cpp
@@ -0,0 +1,92 @@
+#include "billboardPainter.h"
+#include "gfx/models/mesh.h"
+#include "glArrays.h"
+#include "gl_traits.h"
+#include "gldebug.h"
+#include "maths.h"
+#include <gfx/gl/shaders/billboardPainter-frag.h>
+#include <gfx/gl/shaders/billboardPainter-geom.h>
+#include <gfx/gl/shaders/billboardPainter-vert.h>
+#include <stdexcept>
+
+const auto VIEWS = []<GLint... Ep>(std::integer_sequence<GLint, Ep...>) {
+	constexpr float STEP = two_pi / BillboardPainter::VIEW_ANGLES<decltype(two_pi)>;
+	return std::array {rotate_yaw<4>(Ep * STEP)...};
+}(std::make_integer_sequence<GLint, BillboardPainter::VIEW_ANGLES<GLint>>());
+
+BillboardPainter::BillboardPainter() :
+	program {billboardPainter_vert, billboardPainter_geom, billboardPainter_frag}, view {}
+{
+	glDebugScope _ {fbo};
+	glBindFramebuffer(GL_FRAMEBUFFER, fbo);
+	static constexpr std::array<GLenum, 2> ATTACHMENTS {GL_COLOR_ATTACHMENT0, GL_COLOR_ATTACHMENT1};
+	glDrawBuffers(ATTACHMENTS.size(), ATTACHMENTS.data());
+	glReadBuffer(GL_NONE);
+	glBindFramebuffer(GL_FRAMEBUFFER, 0);
+	glUseProgram(program);
+	glUniform(viewLoc, std::span<const glm::mat4> {VIEWS});
+}
+
+void
+BillboardPainter::setView(const glm::mat4 & newView)
+{
+	view = newView;
+}
+
+glTextures<3>
+BillboardPainter::createBillBoardTextures(GLsizei width, GLsizei height)
+{
+	glDebugScope _ {0};
+	glTextures<3> textures;
+	glPixelStorei(GL_UNPACK_ALIGNMENT, 1);
+
+	const auto configuregdata = [width, height](const GLuint texture, const GLint iformat, const GLenum format) {
+		glBindTexture(GL_TEXTURE_2D_ARRAY, texture);
+		glTexParameter(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+		glTexParameter(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+		glTexParameter(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+		glTexParameter(GL_TEXTURE_2D_ARRAY, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+		glTexImage3D(GL_TEXTURE_2D_ARRAY, 0, iformat, width, height, VIEW_ANGLES<GLint>, 0, format, GL_BYTE, nullptr);
+	};
+	configuregdata(textures[0], GL_DEPTH_COMPONENT, GL_DEPTH_COMPONENT);
+	configuregdata(textures[1], GL_RGB8_SNORM, GL_RGB);
+	configuregdata(textures[2], GL_RGB5_A1, GL_RGBA);
+
+	return textures;
+}
+
+void
+BillboardPainter::renderBillBoard(
+		const glTextures<3> & billboard, const MeshBase & mesh, const Texture::AnyPtr texture) const
+{
+	glDebugScope _ {fbo};
+	glEnable(GL_BLEND);
+	glEnable(GL_DEPTH_TEST);
+	glDisable(GL_CULL_FACE);
+	glCullFace(GL_BACK);
+	glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
+	glBindFramebuffer(GL_FRAMEBUFFER, fbo);
+	glClearColor(0, 0, 0, 0);
+	glFramebufferTexture(GL_FRAMEBUFFER, GL_DEPTH_ATTACHMENT, billboard[0], 0);
+	glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, billboard[1], 0);
+	glFramebufferTexture(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT1, billboard[2], 0);
+	if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
+		throw std::runtime_error("Billboard framebuffer not complete!");
+	}
+	if (texture) {
+		texture->bind();
+	}
+	glUseProgram(program);
+	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+	const TextureDimensions billboardSize = {256, 256, 8}; // Texture::getSize(billboard[0]);
+	glViewport(0, 0, billboardSize.x, billboardSize.y);
+	const auto & centre = mesh.getDimensions().centre;
+	const auto & size = mesh.getDimensions().size;
+	glUniform(viewProjectionLoc,
+			std::span<const glm::mat4> {VIEWS *
+					[extentsMat = glm::translate(glm::ortho(-size, size, -size, size, -size, size), -centre), this](
+							const auto & view) {
+						return this->view * view * extentsMat;
+					}});
+	mesh.Draw();
+}
-- 
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