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ifcviewer: draw 3D pivot indicator during navigation

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A small RGB axis cross is rendered at camera_target_ while the user is
orbiting, panning, or has just zoomed.  Visibility toggles on
middle-mouse press/release; the wheel arms a single-shot QTimer that
hides it 750 ms after the last notch.

Drawn in two passes: GL_GREATER at 30% alpha for the occluded portion
(X-ray cue) and GL_LEQUAL at full alpha for the visible portion.  Arm
length is computed from camera_distance_, fovy, and viewport height so
the cross stays ~30 px on screen across zoom levels.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
This commit is contained in:
Dion Moult
2026-04-30 10:21:23 +10:00
parent b9e5739088
commit 1ca2e12f92
2 changed files with 162 additions and 0 deletions
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src/ifcviewer/ViewportWindow.cpp
+138
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@@ -27,6 +27,7 @@
#include <QSurfaceFormat>
#include <QCoreApplication>
#include <QCursor>
#include <QTimer>
#include <QtMath>
#include <QtOpenGL/QOpenGLVersionFunctionsFactory>
@@ -236,6 +237,35 @@ out vec4 frag_color;
void main() { frag_color = vec4(v_color, 1.0); }
)";
// Pivot indicator: a small 3D axis cross drawn at u_pivot in world space.
// a_local is the unit endpoint of one of the six arm vertices (±X,±Y,±Z),
// scaled by u_arm_world so the cross keeps a roughly constant on-screen size
// across zoom levels. Drawing in world space (not screen-aligned) is the
// whole point: it tumbles visibly when the camera orbits, which makes it
// unambiguous that the marker is anchored to a 3D point and not glued to
// the screen. Per-vertex color gives RGB axes matching the corner gizmo.
static const char* PIVOT_VERTEX_SHADER = R"(
#version 450 core
layout(location = 0) in vec3 a_local;
layout(location = 1) in vec3 a_color;
uniform mat4 u_mvp;
uniform vec3 u_pivot;
uniform float u_arm_world;
out vec3 v_color;
void main() {
gl_Position = u_mvp * vec4(u_pivot + a_local * u_arm_world, 1.0);
v_color = a_color;
}
)";
static const char* PIVOT_FRAGMENT_SHADER = R"(
#version 450 core
in vec3 v_color;
uniform float u_alpha;
out vec4 frag_color;
void main() { frag_color = vec4(v_color, u_alpha); }
)";
static GLuint compileShader(QOpenGLFunctions_4_5_Core* gl, GLenum type, const char* source) {
GLuint shader = gl->glCreateShader(type);
gl->glShaderSource(shader, 1, &source, nullptr);
@@ -434,9 +464,12 @@ ViewportWindow::~ViewportWindow() {
}
if (axis_vao_) gl_->glDeleteVertexArrays(1, &axis_vao_);
if (axis_vbo_) gl_->glDeleteBuffers(1, &axis_vbo_);
if (pivot_vao_) gl_->glDeleteVertexArrays(1, &pivot_vao_);
if (pivot_vbo_) gl_->glDeleteBuffers(1, &pivot_vbo_);
if (main_program_) gl_->glDeleteProgram(main_program_);
if (pick_program_) gl_->glDeleteProgram(pick_program_);
if (axis_program_) gl_->glDeleteProgram(axis_program_);
if (pivot_program_) gl_->glDeleteProgram(pivot_program_);
if (pick_fbo_) gl_->glDeleteFramebuffers(1, &pick_fbo_);
if (pick_color_tex_) gl_->glDeleteTextures(1, &pick_color_tex_);
if (pick_depth_rbo_) gl_->glDeleteRenderbuffers(1, &pick_depth_rbo_);
@@ -464,6 +497,7 @@ void ViewportWindow::initGL() {
buildShaders();
buildAxisGizmo();
buildPivotIndicator();
gl_->glEnable(GL_DEPTH_TEST);
gl_->glEnable(GL_MULTISAMPLE);
@@ -570,6 +604,11 @@ void ViewportWindow::buildShaders() {
GLuint fs = compileShader(gl_, GL_FRAGMENT_SHADER, AXIS_FRAGMENT_SHADER);
axis_program_ = linkProgram(gl_, vs, fs);
}
{
GLuint vs = compileShader(gl_, GL_VERTEX_SHADER, PIVOT_VERTEX_SHADER);
GLuint fs = compileShader(gl_, GL_FRAGMENT_SHADER, PIVOT_FRAGMENT_SHADER);
pivot_program_ = linkProgram(gl_, vs, fs);
}
{
GLuint vs = compileShader(gl_, GL_VERTEX_SHADER, HIZ_DOWNSAMPLE_VS);
GLuint fs = compileShader(gl_, GL_FRAGMENT_SHADER, HIZ_DOWNSAMPLE_FS);
@@ -599,6 +638,31 @@ void ViewportWindow::buildAxisGizmo() {
gl_->glVertexArrayAttribBinding(axis_vao_, 1, 0);
}
void ViewportWindow::buildPivotIndicator() {
// 6 verts = 3 line segments along world ±X, ±Y, ±Z, RGB-coded.
static const float verts[] = {
// local x,y,z r,g,b
-1, 0, 0, 1.0f, 0.30f, 0.30f,
1, 0, 0, 1.0f, 0.30f, 0.30f,
0,-1, 0, 0.35f, 0.95f, 0.35f,
0, 1, 0, 0.35f, 0.95f, 0.35f,
0, 0,-1, 0.35f, 0.55f, 1.0f,
0, 0, 1, 0.35f, 0.55f, 1.0f,
};
pivot_rim_count_ = 6; // total vertex count drawn as GL_LINES
gl_->glCreateVertexArrays(1, &pivot_vao_);
gl_->glCreateBuffers(1, &pivot_vbo_);
gl_->glNamedBufferStorage(pivot_vbo_, sizeof(verts), verts, 0);
gl_->glVertexArrayVertexBuffer(pivot_vao_, 0, pivot_vbo_, 0, 6 * sizeof(float));
gl_->glEnableVertexArrayAttrib(pivot_vao_, 0);
gl_->glVertexArrayAttribFormat(pivot_vao_, 0, 3, GL_FLOAT, GL_FALSE, 0);
gl_->glVertexArrayAttribBinding(pivot_vao_, 0, 0);
gl_->glEnableVertexArrayAttrib(pivot_vao_, 1);
gl_->glVertexArrayAttribFormat(pivot_vao_, 1, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float));
gl_->glVertexArrayAttribBinding(pivot_vao_, 1, 0);
}
bool ViewportWindow::growModelVbo(ModelGpuData& m, size_t needed_total) {
size_t new_capacity = m.vbo_capacity;
while (new_capacity < needed_total) new_capacity *= 2;
@@ -2082,6 +2146,7 @@ void ViewportWindow::render() {
hiz_reject_count_.load());
gl_->glBindBuffer(GL_DRAW_INDIRECT_BUFFER, 0);
renderPivotIndicator();
renderAxisGizmo();
// Build HiZ from this frame's resolved depth for next frame's cull.
@@ -2418,6 +2483,69 @@ void ViewportWindow::renderPickPass() {
gl_->glBindFramebuffer(GL_FRAMEBUFFER, 0);
}
void ViewportWindow::renderPivotIndicator() {
if (!pivot_indicator_visible_ || !pivot_program_ || !pivot_vao_) return;
const int h = height() * devicePixelRatio();
if (h <= 0) return;
// Pick a world-space arm length that projects to ~30 pixels at the pivot's
// distance. At fovy=45°, half the visible world height at distance d is
// d * tan(22.5°) ≈ 0.4142 * d. pixels_per_world = (h/2) / (0.4142 * d).
// Inverting: world_per_pixel = 0.8284 * d / h.
const float fovy_rad = qDegreesToRadians(camera_fov_y_deg_);
const float world_per_pixel = camera_distance_ * tanf(fovy_rad * 0.5f) * 2.0f / float(h);
const float arm_pixels = 30.0f * float(devicePixelRatio());
const float arm_world = arm_pixels * world_per_pixel;
const QMatrix4x4 mvp = proj_matrix_ * view_matrix_;
gl_->glUseProgram(pivot_program_);
gl_->glUniformMatrix4fv(gl_->glGetUniformLocation(pivot_program_, "u_mvp"),
1, GL_FALSE, mvp.constData());
gl_->glUniform3f(gl_->glGetUniformLocation(pivot_program_, "u_pivot"),
camera_target_.x(), camera_target_.y(), camera_target_.z());
gl_->glUniform1f(gl_->glGetUniformLocation(pivot_program_, "u_arm_world"),
arm_world);
gl_->glEnable(GL_BLEND);
gl_->glBlendFunc(GL_SRC_ALPHA, GL_ONE_MINUS_SRC_ALPHA);
gl_->glLineWidth(2.0f);
gl_->glBindVertexArray(pivot_vao_);
// Pass 1: occluded portions, depth test reversed, dim — gives an X-ray
// hint that the pivot lives behind geometry.
gl_->glDepthFunc(GL_GREATER);
gl_->glUniform1f(gl_->glGetUniformLocation(pivot_program_, "u_alpha"), 0.30f);
gl_->glDrawArrays(GL_LINES, 0, pivot_rim_count_);
// Pass 2: visible portions, normal depth, full alpha.
gl_->glDepthFunc(GL_LEQUAL);
gl_->glUniform1f(gl_->glGetUniformLocation(pivot_program_, "u_alpha"), 1.0f);
gl_->glDrawArrays(GL_LINES, 0, pivot_rim_count_);
gl_->glBindVertexArray(0);
gl_->glDisable(GL_BLEND);
gl_->glDepthFunc(GL_LESS);
}
void ViewportWindow::setPivotIndicatorVisible(bool visible, int hide_after_ms) {
if (!pivot_indicator_hide_timer_) {
pivot_indicator_hide_timer_ = new QTimer(this);
pivot_indicator_hide_timer_->setSingleShot(true);
connect(pivot_indicator_hide_timer_, &QTimer::timeout, this, [this]() {
pivot_indicator_visible_ = false;
requestUpdate();
});
}
pivot_indicator_visible_ = visible;
if (visible && hide_after_ms > 0) {
pivot_indicator_hide_timer_->start(hide_after_ms);
} else {
pivot_indicator_hide_timer_->stop();
}
}
void ViewportWindow::renderAxisGizmo() {
if (!axis_program_ || !axis_vao_) return;
const int dpr = devicePixelRatio();
@@ -2475,6 +2603,10 @@ void ViewportWindow::handleMousePress(QMouseEvent* e) {
}
active_button_ = e->button();
last_mouse_pos_ = e->pos();
if (e->button() == Qt::MiddleButton) {
setPivotIndicatorVisible(true);
requestUpdate();
}
}
void ViewportWindow::handleMouseRelease(QMouseEvent* e) {
if (camera_mode_ == CameraMode::Fps) return;
@@ -2484,7 +2616,12 @@ void ViewportWindow::handleMouseRelease(QMouseEvent* e) {
emit objectPicked(id);
requestUpdate(); // selection highlight changed
}
const bool was_navigating = (active_button_ == Qt::MiddleButton);
active_button_ = Qt::NoButton;
if (was_navigating && pivot_indicator_visible_) {
setPivotIndicatorVisible(false);
requestUpdate();
}
}
void ViewportWindow::handleMouseMove(QMouseEvent* e) {
if (camera_mode_ == CameraMode::Fps) {
@@ -2550,5 +2687,6 @@ void ViewportWindow::handleWheel(QWheelEvent* e) {
float factor = e->angleDelta().y() > 0 ? 0.9f : 1.1f;
camera_distance_ *= factor;
camera_distance_ = qMax(0.1f, camera_distance_);
setPivotIndicatorVisible(true, 750);
requestUpdate();
}