PortalGame/src/gfx/renderer.cpp

#include "renderer.hpp"

#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>

#include "gl.hpp"

#include "gfx/shader_sources.hpp"

gfx::Renderer::Renderer()
{
	ShaderSources::MakeShader(sector_shader_, SS_SECTOR_MESH_VERT, SS_SECTOR_MESH_FRAG);
	ShaderSources::MakeShader(portal_shader_, SS_PORTAL_VERT, SS_PORTAL_FRAG);
	proj_ = glm::mat4(1.0f); // Initialize projection matrix to identity

	SetupPortalVAO();
}

void gfx::Renderer::SetupPortalVAO()
{
	const glm::vec3 portal_verts[4] = {
		{ -0.5f, 0.0f,  0.5f }, // Top-left
		{ -0.5f, 0.0f, -0.5f }, // Bottom-left
		{  0.5f, 0.0f, -0.5f }, // Bottom-right
		{  0.5f, 0.0f,  0.5f }, // Top-right
	};

	portal_vao_ = std::make_shared<VertexArray>(VA_POSITION, 0);
	portal_vao_->SetVBOData(portal_verts, sizeof(portal_verts));
}

void gfx::Renderer::Begin(size_t width, size_t height)
{
	glViewport(0, 0, width, height);
	glClearStencil(0);
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
}

void gfx::Renderer::DrawWorld(
	const game::World& world,
	size_t sector_idx,
	const glm::vec3& eye,
	const glm::vec3& dir,
	const glm::vec3& up,
	float aspect,
	float fov)
{
	proj_ = glm::perspective(
		glm::radians(fov), // FOV
		aspect,             // Aspect ratio
		0.1f,              // Near plane
		1000.0f             // Far plane
	);

	glm::mat4 view = glm::lookAt(
		eye,               // Camera position
		eye + dir,        // Look at point (camera position + look direction)
		up                 // Up vector
	);

	glEnable(GL_DEPTH_TEST);
	glDepthFunc(GL_LESS);

	glEnable(GL_CULL_FACE);
	glCullFace(GL_BACK);

	glEnable(GL_STENCIL_TEST);
	glStencilFunc(GL_ALWAYS, 0, 0xFF); // Always pass stencil test
	glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
	glStencilMask(0xFF);

	const game::Sector& sector = world.GetSector(sector_idx);

	DrawSectorParams params;
	params.sector = &sector;
	params.entry_portal = nullptr; // No entry portal for the first sector
	params.clip_plane = glm::vec4(0.0f, 0.0f, 1.0f, 1000.0f); // Default clip plane
	params.screen_aabb = collision::AABB2(glm::vec2(-1.0f), glm::vec2(1.0f)); // Full screen
	params.recursion = 0; // Start with recursion level 0
	params.view = view;
	params.view_proj = proj_ * view;
	params.eye = eye;
	
	DrawSector(params);

	//glDisable(GL_STENCIL_TEST);
	//glDisable(GL_CULL_FACE);
	//glDisable(GL_DEPTH_TEST);

}

void gfx::Renderer::DrawSector(const DrawSectorParams& params)
{
	assets::Mesh& mesh = *params.sector->GetMesh();

	glm::mat4 model = glm::mat4(1.0f); // Identity matrix for model



// #ifndef PG_GLES
// 	glEnable(GL_CLIP_DISTANCE0);
// #else
// 	glEnable(GL_CLIP_DISTANCE0_EXT);
// #endif

	glUseProgram(sector_shader_->GetId());
	glUniformMatrix4fv(sector_shader_->U(gfx::SU_VIEW_PROJ), 1, GL_FALSE, &params.view_proj[0][0]);
	glUniformMatrix4fv(sector_shader_->U(gfx::SU_MODEL), 1, GL_FALSE, &model[0][0]);
	glUniform4fv(sector_shader_->U(gfx::SU_CLIP_PLANE), 1, &params.clip_plane[0]);

	glBindVertexArray(mesh.GetVA().GetVAOId());
	for (auto mesh_materials = mesh.GetMaterials(); const auto& mat : mesh_materials) {
		glActiveTexture(GL_TEXTURE0);
		if (mat.texture) {
			glBindTexture(GL_TEXTURE_2D, mat.texture->GetId());
			glUniform1i(sector_shader_->U(gfx::SU_TEX), 0); // Bind texture to sampler
		}
		else {
			glBindTexture(GL_TEXTURE_2D, 0); // No texture
		}
		glDrawElements(GL_TRIANGLES, mat.num_tris * 3, GL_UNSIGNED_INT, (void*)(mat.first_tri * 3 * sizeof(uint32_t)));
	}
	glBindVertexArray(0);

	for (size_t i = 0; i < params.sector->GetNumPortals(); ++i)
	{
		const game::Portal& portal = params.sector->GetPortal(i);
		DrawPortal(params, portal);
	}

}

void gfx::Renderer::DrawPortal(const DrawSectorParams& params, const game::Portal& portal)
{
	if (params.recursion > 10)
	{
		return; // Recursion limit reached
	}

	if (&portal == params.entry_portal)
	{
		return; // Skip the portal this sector was rendered through
		// This should NEVER happen due to portal plane check, but would cause cyclic traversal if it did.
	}

	if (!portal.link)
	{
		return; // Portal not linked, skip
	}

	// Signed distance of eye to the portal plane
	float eye_plane_sd = glm::dot(glm::vec3(portal.plane), params.eye) + portal.plane.w;
	if (eye_plane_sd < 0.0f)
	{
		return; // Eye is behind the portal plane, skip
	}

	collision::AABB2 portal_aabb;
	if (!ComputePortalScreenAABB(portal, params.view_proj, portal_aabb))
	{
		return; // Portal is fully behind the camera, skip
	}

	if (!portal_aabb.CollidesWith(params.screen_aabb))
	{
		return; // Portal AABB does not intersect with the screen AABB, skip
	}

	// Open portal
	glStencilFunc(GL_EQUAL, params.recursion, 0xFF);
	glStencilOp(GL_KEEP, GL_KEEP, GL_INCR);
	glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
	DrawPortalPlane(params, portal, false); // Mark the portal plane in stencil buffer
	glStencilFunc(GL_EQUAL, params.recursion + 1, 0xFF);
	glStencilOp(GL_KEEP, GL_KEEP, GL_KEEP);
	glDepthFunc(GL_ALWAYS);
	DrawPortalPlane(params, portal, true); // Clear the depth buffer for nested sector
	glDepthFunc(GL_LESS);
	glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);

	const game::Portal& other_portal = *portal.link;
	const game::Sector& other_sector = *other_portal.sector;

	DrawSectorParams new_params;
	new_params.sector = &other_sector;
	new_params.entry_portal = &other_portal;
	new_params.clip_plane = other_portal.plane; // Use the portal plane as the clip plane

	// Compute the new screen AABB based on the portal AABB and the current screen AABB
	new_params.screen_aabb = params.screen_aabb.Intersection(portal_aabb);

	new_params.recursion = params.recursion + 1;
	new_params.view = params.view * other_portal.link_trans;
	new_params.view_proj = proj_ * new_params.view;
	new_params.eye = portal.link_trans * glm::vec4(params.eye, 1.0f);

	// Draw the sector through the portal
	DrawSector(new_params);

	// Close portal
	glStencilOp(GL_KEEP, GL_KEEP, GL_DECR);
	glColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_FALSE);
	glStencilFunc(GL_EQUAL, params.recursion + 1, 0xFF);
	DrawPortalPlane(params, portal, false);
	glColorMask(GL_TRUE, GL_TRUE, GL_TRUE, GL_TRUE);
}

bool gfx::Renderer::ComputePortalScreenAABB(const game::Portal& portal, const glm::mat4 view_proj, collision::AABB2& aabb)
{
	size_t num_behind = 0;

	for (size_t i = 0; i < 4; ++i)
	{
		glm::vec4 vert = glm::vec4(portal.verts[i], 1.0f);
		glm::vec4 clip = view_proj * vert;
		
		if (clip.w <= 0.0f)
		{
			num_behind++;
			continue; // Skip vertices behind the camera
		}
		
		glm::vec2 ndc = clip;
		ndc /= clip.w;

		aabb.AddPoint(ndc, 0.0f);
	}

	if (num_behind == 4)
	{
		return false; // All vertices are behind the camera, no visible portal
	}

	if (num_behind > 0)
	{
		// Some vertices are behind the camera, cannot use the AABB
		aabb = collision::AABB2(glm::vec2(-1.0f), glm::vec2(1.0f)); // Full screen AABB
	}

	return true;
}

void gfx::Renderer::DrawPortalPlane(const DrawSectorParams& params, const game::Portal& portal, bool clear_depth)
{
	if (!clear_depth) // first draw
	{
		glUseProgram(portal_shader_->GetId());
		glUniformMatrix4fv(portal_shader_->U(gfx::SU_VIEW_PROJ), 1, GL_FALSE, &params.view_proj[0][0]);
		glUniformMatrix4fv(portal_shader_->U(gfx::SU_MODEL), 1, GL_FALSE, &portal.trans[0][0]);
		glUniform4fv(portal_shader_->U(gfx::SU_CLIP_PLANE), 1, &params.clip_plane[0]);
		glUniform2fv(portal_shader_->U(gfx::SU_PORTAL_SIZE), 1, &portal.def->size[0]);
		glUniform1i(portal_shader_->U(gfx::SU_CLEAR_DEPTH), 0);

		glBindVertexArray(portal_vao_->GetVAOId());
	}
	else // assume uniforms are already set from previous draw
	{ 
		glUniform1i(portal_shader_->U(gfx::SU_CLEAR_DEPTH), 1);
	}
	glDrawArrays(GL_TRIANGLE_FAN, 0, 4); // Draw the portal as a quad
}