Ok so here is my try to write a small example on creating a basic mesh dynamically.
I have done it by reading what I could find about the topic and a lot of experimenting.
Please let me know if I have done some mistakes in my asumptions here, thanks!
Also, how can I get the camera to mimic the result/view from setMatricesWindow( getWindowSize() ) ?
#include "cinder/app/App.h"
#include "cinder/app/RendererGl.h"
#include "cinder/gl/gl.h"
#include "cinder/CinderImGui.h"
using namespace ci;
using namespace ci::app;
/*
Creates a basic Mesh as a TriMesh or a VboMesh.
-----------------------------------------------
1) Defines 3 vertex positions and then defines a triangle polygon from them.
2) A Left Mouse Click -> Creates another vertex and another triangle,
using the new vertex and two of the existing vertices.
3) A Right Mouse Click deletes the second triangle and the last vertex in this mesh.
*/
class BasicMeshApp : public App {
public:
void setup() override;
void update() override;
void draw() override;
void mouseDown(MouseEvent event) override;
void resize() override;
void buildTriMesh();
void buildVboMesh();
vec2 mousePos;
std::list <vec3> mousePoints; // List with XYZ positions
bool useTriMesh = false;
bool useVboMesh = false;
bool useAnimation = true;
bool useWireframe = false;
// TriMesh
TriMesh mTriMesh; // Handle to the TriMesh
/// VboMesh
gl::VboMeshRef mVboMesh; // Reference to the VboMesh
std::vector<vec3> positions; // Vector(List) for XYZ positions
std::vector<ColorA> colors; // Vector(List) for colors
std::vector<uint32_t> indices; // Vector(List) for indices (to create polygons) ( uint32_t is a fixed width integer type )
gl::VboRef indexBufferObj; // Reference to a Vertex Buffer to store the indices
gl::BatchRef batchVbo; // Reference to the Batch
};
void BasicMeshApp::resize() {
// Rebuild the mesh just to fit the window...
buildTriMesh(); // Create the TriMesh
buildVboMesh(); // Create the VboMesh
update(); // Keep drawing the ImGui interface while resizing
}
void BasicMeshApp::mouseDown(MouseEvent event)
{
// Add or remove points:
if (event.isLeft()) { // Left mouse-click?
mousePoints.clear(); // Clear the list (Just to keep it simple)
// Add a new point to the list:
mousePoints.push_front(vec3(event.getPos().x, event.getPos().y, 0));
}
else if (event.isRight()) { // Right mouse-click?
if (mousePoints.size() > 0) { // If there still points in the List...
// Remove one point from the list:
mousePoints.pop_front();
}
}
buildTriMesh(); // Recreate the mesh
buildVboMesh(); // Recreate the mesh
}
void BasicMeshApp::buildTriMesh()
{
// Remove old data
mTriMesh.clear();
// Setup the TriMesh format: (Choose the attributes that you will need)
mTriMesh = TriMesh(
TriMesh::Format() // This TriMesh shall contain:
.positions() // Position
.colors(3) // RGB Color ?? Couldn't use .colors(4) Why...?
);
// *** Build the first triangle polygon ***
// Vertex 1
mTriMesh.appendPosition(vec3(getWindowCenter().x, getWindowCenter().y -20, 0)); // Position
mTriMesh.appendColorRgb(Color(0, 0, 1)); // Color ?? Couldn't use ColorA(0, 0, 1, 0.5) Why...?
// Vertex 2
mTriMesh.appendPosition(vec3(0, 0, 0));
mTriMesh.appendColorRgb(Color(0, 1, 1));
// Vertex 3
mTriMesh.appendPosition(vec3(getWindowWidth(), 0, 0));
mTriMesh.appendColorRgb(Color(1, 0, 1));
// Create the first triangle polygon (from the 3 first vertices/indicies)
mTriMesh.appendTriangle(0, 1, 2); // Use indices/vertices 1,2,3
// *** Build the second triangle polygon ***
if (mousePoints.size() > 0) { // If there have been drawn an extra vertex...
// Vertex 4 (Takes the position from the list with mouse-clicks)
mTriMesh.appendPosition(vec3(mousePoints.front().x, mousePoints.front().y, 0));
mTriMesh.appendColorRgb(Color(0.5, 0.5, 0.5));
// Create the second triangle polygon (from the 2 first vertices and the new 4:th vertex)
mTriMesh.appendTriangle(0, 1, 3); // Use indices/vertices 1,2 and 4
}
}
void BasicMeshApp::buildVboMesh() {
// Clear all previous mesh data: <-- (Just to keep it simple)
positions.clear();
colors.clear();
indices.clear();
// Define a VboMesh Layout: (Choose the attributes that you will need)
std::vector<gl::VboMesh::Layout> layout = {
gl::VboMesh::Layout().usage(GL_DYNAMIC_DRAW).attrib(geom::Attrib::POSITION, 3), // *Dynamic* positions (Will be animated)
gl::VboMesh::Layout().usage(GL_STATIC_DRAW).attrib(geom::Attrib::COLOR, 4) // *Static* Colors (Will not animate)
// .attrib(geom::TEX_COORD_0, 2)
// .attrib(geom::NORMAL, 3)
};
// *** Build the first triangle polygon ***
// Vertex 1
positions.push_back(vec3(getWindowCenter().x, getWindowCenter().y +20, 0)); // Add a vertex position element to the positions vector/List
colors.push_back(ColorA(1, 0, 0, 1)); // Add a vertex color element to the color vector/List
indices.push_back(0); // Add first index for the first triangle polygon
// Vertex 2
positions.push_back(vec3(ci::app::getWindowWidth(), ci::app::getWindowHeight(), 0));
colors.push_back(ColorA(0.5, 0.5, 0, 1));
indices.push_back(1); // Second index for the first triangle polygon
// Vertex 3
positions.push_back(vec3(0, ci::app::getWindowHeight(), 0));
colors.push_back(ColorA(0, 0.5, 0.5, 1));
indices.push_back(2); // Last index for the first triangle polygon
// *** Build the second triangle polygon ***
if (mousePoints.size() > 0) { // If there have been drawn an extra vertex
// Vertex 4 (Takes the position from the list with mouse-clicks)
positions.push_back( vec3( mousePoints.front().x, mousePoints.front().y, 0));
colors.push_back(ColorA(0.5, 0.5, 0.5, 1));
// Create the second triangle polygon from these indices:
indices.push_back(0); // First index for the second polygon/triangle (Vertex 1) (Using same position as vertex 1)
indices.push_back(1); // Second index for the second polygon/triangle (Vertex 2) (Using same position as vertex 2)
indices.push_back(3); // Last index for the second polygon/triangle (Vertex 4) (Using same position as vertex 4, wich was the mouse click)
}
// Allocate a Vertex Buffer to store the indices on the GPU (So the Vbo-mesh knows from wich vertices it should build its triagles)
indexBufferObj = gl::Vbo::create(GL_ELEMENT_ARRAY_BUFFER, indices, GL_STATIC_DRAW); // ? GL_STATIC_DRAW ? GL_DYNAMIC_DRAW GL_ARRAY_BUFFER
// Create the Vbo-mesh and pass the index-BufferObject
mVboMesh = gl::VboMesh::create(positions.size(), GL_TRIANGLES, { layout }, indices.size(), GL_UNSIGNED_INT, indexBufferObj);
// GL_LINES GL_TRIANGLES GL_POINTS GL_UNSIGNED_SHORT
mVboMesh->bufferAttrib<vec3>(geom::POSITION, positions); // Hook up the positions vector/List to the VBO-mesh
mVboMesh->bufferAttrib<ColorA>(geom::COLOR, colors); // Hook up the color vector/List to the VBO-mesh
batchVbo = gl::Batch::create(mVboMesh, gl::getStockShader(gl::ShaderDef().color())); // Create a (faster) Batch object from the Vbo-mesh (A Batch combines the mesh with the shader)
//batchVbo = gl::Batch::create(mVboMesh, gl::getStockShader( gl::ShaderDef().lambert().color()) ); // Alternative batch that use the built in Lambert shader
}
void BasicMeshApp::setup()
{
ImGui::Initialize();
gl::pointSize(6);
buildTriMesh(); // Create the TriMesh
buildVboMesh(); // Create the VboMesh
}
void BasicMeshApp::update()
{
// ImGui interface
ImGui::Begin("Settings - Mesh");
ImGui::SetWindowPos(ImVec2(10, 10), ImGuiCond_FirstUseEver);
ImGui::SetWindowSize(ImVec2(190, 140), ImGuiCond_FirstUseEver);
static int e = 0;
ImGui::RadioButton("Use TriMesh (CPU-mem)", &e, 0);
ImGui::RadioButton("Use VboMesh (GPU-mem)", &e, 1);
if (e == 0)
{
useTriMesh = true;
useVboMesh = false;
}
else
{
useTriMesh = false;
useVboMesh = true;
}
ImGui::NewLine();
ImGui::Checkbox("Animate Vbo", &useAnimation);
ImGui::Checkbox("Wireframe", &useWireframe);
ImGui::End();
}
void BasicMeshApp::draw()
{
gl::clear();
// reset the matrices
gl::setMatricesWindow(getWindowSize());
/* CameraPersp cam;
cam.lookAt(vec3(0, 0, -900), vec3(0)); // ?? How to "flip/mirror" the cam to mimic the result from gl::setMatricesWindow(getWindowSize()) ??
gl::setMatrices(cam); */
if (useWireframe) gl::enableWireframe();
else gl::disableWireframe();
// Draw the TriMesh
if (useTriMesh)
{
gl::draw(mTriMesh); // Draw the TriMesh
}
// Draw the VboMesh
if (useVboMesh)
{
if (useAnimation) // First animate the Vbo mesh vertex positions
{
// Get a Position Attribute reference to the GPU buffer
auto mappedPosAttrib = mVboMesh->mapAttrib3f(geom::Attrib::POSITION, false);
// Add animated displacement to the positionAttribute for the first vertex position in the buffer
mappedPosAttrib->y = getWindowCenter().y + sin(getElapsedSeconds() *8) *10;
mappedPosAttrib->x = getWindowCenter().x + cos(getElapsedSeconds() *8) *10;
mappedPosAttrib.unmap();
}
// gl::draw(mVboMesh); // Draw the VboMesh
batchVbo->draw(); // Draw the VboMesh (faster) with a "Batch"
}
// Draw text
if (useWireframe) gl::disableWireframe(); // (Turn off wireframe now while drawing text)
if (mousePoints.size() == 0) gl::drawString("Left click to: \nAdd a vertex", vec3(20, getWindowCenter().y -20, 0), ColorA(1, 1, 1, 0.5), Font("verdana", 20.f));
if (mousePoints.size() >= 1) gl::drawString("Left click to: \nSet a new position", vec3(20, getWindowCenter().y - 20, 0), ColorA(1, 1, 1, 0.5), Font("verdana", 20.f));
if (mousePoints.size() >= 1)gl::drawStringCentered("Right click to: \nRemove the vertex", vec3(getWindowWidth()-100, getWindowCenter().y - 20, 0), ColorA(1, 1, 1, 0.5), Font("verdana", 20.f));
if (useTriMesh) gl::drawStringCentered("TriMesh", vec3(getWindowCenter().x, 20, 0), Color(1, 1, 1), Font("verdana", 50.f));
if (useVboMesh) gl::drawStringCentered("VboMesh", vec3(getWindowCenter().x, getWindowHeight() -50, 0), Color(1, 1, 1), Font("verdana", 50.f));
gl::color(Color(1, 1, 0.0)); // Set a yellow draw color
// Draw Points (from the mousePoints list)
gl::begin( GL_POINTS );
for each( vec3 point in mousePoints ) {
gl::vertex( point ); // Draw each point in the list
}
/*
// Draw all points in the TriMesh
if (useTriMesh)
{
vec3* allVertexPositions;
allVertexPositions = mTriMesh.getPositions<3>();
for (int i = 0; i < mTriMesh.getBufferPositions().size() / 3; i++)
{
gl::vertex(allVertexPositions->x, allVertexPositions->y, 0); // Draw this vertex position as a Point
allVertexPositions++;
}
}
// Draw all points in the VboMesh
if (useVboMesh)
{
gl::VboMesh::MappedAttrib allVertexPositions = mVboMesh->mapAttrib3f(geom::Attrib::POSITION, false);
for (int i = 0; i < mVboMesh->getNumVertices() ; i++)
{
gl::vertex(allVertexPositions->x, allVertexPositions->y, 0); // Draw this vertex position as a Point
allVertexPositions++;
}
allVertexPositions.unmap();
}*/
gl::end();
}
CINDER_APP( BasicMeshApp, RendererGl( RendererGl::Options().msaa( 0 ) ) )
In plain C++ I would just create two Lists → Vertices & Triangles and add or remove members to them as I needed.
when I use setMatrices(camera) so then I have to invert the FOV to make it look right. That is most likely not the correct way to do it? 
The ‘flipping problem’ comes right after using use setMatrices(camera), so maybe I just should use the camera in another way?