I have a dynamic body with many polygon shapes for my game character. In order to turn back the game character I flip vertices using this code:
void Box2dManager::flipFixtures(bool horizzontally, b2Body* physBody)
{
b2Fixture* fix = physBody->GetFixtureList();
while(fix)
{
b2Shape* shape = fix->GetShape();
if(shape->GetType()== b2Shape::e_polygon)
{
// flipping x or y coordinates
b2PolygonShape* ps = (b2PolygonShape*)shape;
for(int i=0; i < ps->GetVertexCount(); i++)
horizzontally ? ps->m_vertices[i].x *= -1 : ps->m_vertices[i].y *= -1;
// revert the vertices (no need after Box2D 2.3.0 as polygon creation computes the convex hull)
b2Vec2* reVert = new b2Vec2[ps->GetVertexCount()];
int j = ps->GetVertexCount() -1;
for(int i=0; i<ps->GetVertexCount();i++)
reVert[i] = ps->m_vertices[j--];
ps->Set(&reVert[0], ps->GetVertexCount());
}
fix = fix->GetNext();
}
}
I also have static edge shapes as walls. And it happens, that when I flip the character, sometimes vertices of the same polygon appear to be in different sides of the same static edge shape. As a result my character sticks to the wall (it is being trapped in the static edge shape). How I should handle this situation?
Related
I am designing a 2d platformer tile-based game using SDL. I am having trouble with converting from world coordinates to screen coordinates. I defined (0, 0) as the top left for both the screen and the world and (x, y) as the bottom right.
Currently, I am storing the map data like so:
"." is an air tile
"#" is a grass tile
"i" is an iron tile
"p" is a wooden plank tile
"c" is the top layer of the ice
"b" is the bottom layers of the ice
...iiiiii...pppppp..cccccc...........................................
...iiiiii...pppppp..b....b...........................................
...iiiiii...p....p..b....b...........................................
...iiiiii...p....p..b....b...........................................
...iiiiii...p....p..b....b...........................................
...iiiiii...p....p..b....b...........................................
...iiiiii...p....p..bbbbbb...........................................
...iiiiii...pppppp..bbbbbb...........................................
...iiiiii...pppppp..bbbbbb...........................................
...iiiiii...pppppp..bbbbbb...........................................
...iiiiii...pppppp..bbbbbb...........................................
...iiiiii...pppppp..bbbbbb...........................................
#####################################################################
.....................................................................
.....................................................................
.....................................................................
.....................................................................
.....................................................................
.....................................................................
.....................................................................
.....................................................................
.....................................................................
.....................................................................
.....................................................................
....................................................................#
I am loading the map like so, in which the top left is (0, 0):
typedef struct Tile {
char texture_id;
int x;
int y;
} Tile;
Map::Map(std::string raw_map_data) {
// Initialize private variables
this->unparsed_map_data= raw_map_data;
// Split the map data into a std::vector<std::string> based off of newlines
std::vector<std::string> map_data_split = split_string(raw_map_data, "\n");
// Next, convert the map data to a vector Tile structs
int cur_x = 0;
int cur_y = 0;
std::vector<Tile> tiles_processed;
Tile tile;
for (size_t i = 0; i < map_data_split.size(); i++) {
for (size_t j = 0; j < map_data_split[i].size(); j++) {
tile.x = cur_x;
tile.y = cur_y;
tile.texture_id = map_data_split[i][j];
tiles_processed.push_back(tile);
cur_x += TILE_WIDTH;
}
cur_x = 0;
cur_y += TILE_HEIGHT;
}
this->tiles_parsed = tiles_processed;
//std::reverse(this->tiles_parsed.begin(), this->tiles_parsed.end());
DebugTiles(this->tiles_parsed); // DEBUG: used to print tiles to find errors
}
I have set the camera coordinates as the world coordinates of the top-left point of the window. Additionally, the player never leaves the center of the screen. Furthermore, the transformation that I am using to go from the world coordinates to the screen coordinates is as follows: screen coordinates = camera coordinates - world coordinates of tile
void Camera::Render(std::vector<Tile> tiles_to_render, SDL_Texture* player_texture) {
// Render the scene
for (size_t i = 0; i < tiles_to_render.size(); i++) {
if (tiles_to_render[i].texture_id != '.') {
// world_pos_tl is an SDL_Rect containing the camera coordinates
SDL_Rect dstrect = {this->world_pos_tl.x - tiles_to_render[i].x, this->world_pos_tl.y - tiles_to_render[i].y, TILE_WIDTH, TILE_HEIGHT};
SDL_RenderCopy(this->renderer, this->textures[tiles_to_render[i].texture_id], NULL, &dstrect);
}
}
// Render the character (always in center of screen)
SDL_Rect player_dstrect = {(WIDTH / 2) - TILE_WIDTH, (HEIGHT / 2) - TILE_HEIGHT, TILE_WIDTH, TILE_HEIGHT};
SDL_RenderCopy(this->renderer, player_texture, NULL, &player_dstrect);
}
However, when I compile and run, I get the following result, as the world is rotated 270 degrees.
The result of running the code:
Special thanks to Gorbit99 on the "One Lone Coder" discord server who figured this out for me.
The issue is that it is supposed to be screen position = world position - camera position. The reason for this is because when you move an object to the left and the camera stays still, the object should move left. But if the camera moves to the left and the object stays still, it should look like the object's moving to the right.
Side note: I am overusing the keyword, this a lot, as it is only meant to be used when a variable in a function has the same name as a class member and you want to specify that you want to use the class member. Therefore, in practice, the keyword this should rarely be used.
While I found many problems that are similar too mine, none of the solutions solved my problem.
I've been experimenting with SDL2 in C++ (Visual C++) and the entity-component-system (ECS). But I just can't figure out the bug in my collision response.
So here it is: My player sometimes gets set back to its origin when it encounters something like a rock (a simple gray tile). But sometimes it goes right through and gets stuck or ends up on the other side.
I can only assume it has something to do with the data changed in between frames, so it isn't always caught. But for the life of me I can't figure it out.
Here is my rectangular detection method:
bool Collision::RectIntersect(const SDL_Rect& a, const SDL_Rect& b, SDL_Rect& intersect)
{
intersect = { 0, 0, 0, 0 };
int leftX = std::max(a.x, b.x);
int rightX = std::min(a.x + a.w, b.x + b.w);
int topY = std::max(a.y, b.y);
int bottomY = std::min(a.y + a.h, b.y + b.h);
if (leftX < rightX && topY < bottomY)
{
intersect = { leftX, topY, rightX - leftX, bottomY - topY };
return true;
}
return false;
}
Here is my snippet where my inputs are handled and subsequently any collision detections are resolved before the code actually moves anything:
void InputComponent::handleEvents(SDL_Event* e)
{
const Uint8 *keyboardState = SDL_GetKeyboardState(NULL);
if (e != nullptr)
{
/*
keyHeld: array of 4 for each direction (+/- x, +/- y (WASD))
hold value true, if pressed down, otherwise false
*/
if (keyboardState[SDL_SCANCODE_A])
{
keyHeld[0] = true;
}
else
{
keyHeld[0] = false;
}
if (keyboardState[SDL_SCANCODE_D])
{
keyHeld[1] = true;
}
else
{
keyHeld[1] = false;
}
if (keyboardState[SDL_SCANCODE_W])
{
keyHeld[2] = true;
}
else
{
keyHeld[2] = false;
}
if (keyboardState[SDL_SCANCODE_S])
{
keyHeld[3] = true;
}
else
{
keyHeld[3] = false;
}
}
/*
tmpVel: Vector to store the assumed velocity in x- and y-direction
*/
Vector2D tmpVel(0.0f, 0.0f);
// left and right (A and D)
if (keyHeld[0] && !keyHeld[1]) // left
{
tmpVel.x = -1.0f;
}
else if (!keyHeld[0] && keyHeld[1]) // right
{
tmpVel.x = 1.0f;
}
else
{
tmpVel.x = 0.0f; // left and right cancel each other out
}
// up and down (W and S)
if (keyHeld[2] && !keyHeld[3]) // up
{
tmpVel.y = -1.0f;
}
else if (!keyHeld[2] && keyHeld[3]) // down
{
tmpVel.y = 1.0f;
}
else
{
tmpVel.y = 0.0f; // up and down cancel each other out
}
/*
check for collision with presumed direction according to tmpVel
*/
SDL_Rect intersection;
// get current player position
SDL_Rect movedPlayer = entity->getComponent<CollisionComponent>().getCollider();
// add trajectory of theoretical movement
movedPlayer.x += static_cast<int>(tmpVel.x * vel_->getSpeed());
movedPlayer.y += static_cast<int>(tmpVel.y * vel_->getSpeed());
bool hasCollided = false;
// collect all collidable objects
for (auto& c : manager_->getGroup(GroupLabel::GR_COLLIDERS))
{
// check player against each collidable tile
//if (SDL_IntersectRect(&movedPlayer, &c->getComponent<CollisionComponent>().getCollider(), &intersection))
if (Collision::RectIntersect(movedPlayer, c->getComponent<CollisionComponent>().getCollider(), intersection))
{
// collision on x-axis
if (intersection.w > 0)
{
// set velocity on x-axis to 0
vel_->setVelocityX(0.0f);
// reset player position back according to width of intersected rectangle
pos_->setPosX(pos_->getPos().x + (static_cast<float>(intersection.w) * (-tmpVel.x)));
}
// collision on y-axis
if (intersection.h > 0)
{
// set velocity on y-axis to 0
vel_->setVelocityY(0.0f);
// reset player position back according to height of intersected rectangle
pos_->setPosY(pos_->getPos().y + (static_cast<float>(intersection.h) * (-tmpVel.y)));
}
hasCollided = true;
}
}
if (!hasCollided)
{
vel_->setVelocity(tmpVel);
}
}
Can anybody put me in the right direction?
What happens when the right edge of the player exactly equals the left edge of the rock? It looks like the collision is not detected, since the test is for (leftX < rightX). So the velocity is updated and the player is moved by the velocity. (It's odd that you simply update the velocity and later move the player instead of just moving them to the new already calculated position.) If you change the check to (leftX <= rightX), does the problem persist?
As far as I can see there are two things wrong with your collision detection. The first is that you're testing (leftX < rightX && topY < bottomY) when you should be testing (leftX <= rightX && topY <= bottomY). If you fix this your code will work in most situations.
The second problem you've got, which may not become apparent straight away, is that your are performing collision detection for discreet points in time. If your player has a large enough velocity vector you may end up with this situation:
Update 1: Player is in front of wall travelling towards it. AABB test shows no collision.
Update 2: Player is behind wall travelling away from it. AABB test shows no collision.
Your AABB test is correct and yet the player has passed through the wall. The naive approach to fixing this is to test more often (update 1.5 may have shown a collision), or to limit player velocity. Both approaches will require a lot of fine tuning especially if you're dealing with objects that can move at different speeds and walls with differing thickness.
A more robust approach is to take account of velocity in your test. Since you know the velocity of your AABB you can project this shape along its velocity vector. If you do this for both AABBs you'll end up with two elongated shapes which you can test against each other. If they overlap then you know that their paths cross and that there may be a collision.
Of course, knowing that there might be a collision is not hugely helpful. The problem is one AABB may be moving very slowly and the other very quickly so even though they both pass through the same space (their elongated shapes intersect) they don't pass through it at the same time.
Figuring out whether they both pass through the same space at the same time is hard, so instead we cheat. If you subtract the velocity of B from the velocity of A and then use this modified velocity to project the elongated shape of A, you can effectively treat B as a stationary object and still get the correct result. Knowing this, your test is now "does B overlap the elongated shape of A?". This is just a simple AABB vs Ngon problem.
While the above will give you a boolean as to whether two moving AABBs collide it will not tell you when they collide which is also useful for calculating things like rebounds.
I would very much recommend the book Real Time Collision Detection by Christer Ericson which is pretty much the go to book on collision detection for any aspiring game developer.
The following is a code snippet from the CD-ROM which accompanies the book. It tests a moving AABB against another moving AABB and also provides a time of first contact.
// Intersect AABBs ‘a’ and ‘b’ moving with constant velocities va and vb.
// On intersection, return time of first and last contact in tfirst and tlast
int IntersectMovingAABBAABB(AABB a, AABB b, Vector va, Vector vb, float &tfirst, float &tlast)
{
// Exit early if ‘a’ and ‘b’ initially overlapping
if (TestAABBAABB(a, b)) {
tfirst = tlast = 0.0f;
return 1;
}
// Use relative velocity; effectively treating ’a’ as stationary
Vector v = vb - va;
// Initialize times of first and last contact
tfirst = 0.0f;
tlast = 1.0f;
// For each axis, determine times of first and last contact, if any
for (int i = 0; i < 3; i++) {
if (v[i] < 0.0f) {
if (b.max[i] < a.min[i]) return 0;
// Nonintersecting and moving apart
if (a.max[i] < b.min[i]) tfirst = Max((a.max[i] - b.min[i]) / v[i], tfirst);
if (b.max[i] > a.min[i]) tlast = Min((a.min[i] - b.max[i]) / v[i], tlast);
}
if (v[i] > 0.0f) {
if (b.min[i] > a.max[i]) return 0;
// Nonintersecting and moving apart
if (b.max[i] < a.min[i]) tfirst = Max((a.min[i] - b.max[i]) / v[i], tfirst);
if (a.max[i] > b.min[i]) tlast = Min((a.max[i] - b.min[i]) / v[i], tlast);
}
// No overlap possible if time of first contact occurs after time of last contact
if (tfirst > tlast) return 0;
}
return 1;
}
The following attribution is required by Elsevier's Software License Agreement:
“from Real-Time Collision Detection by Christer Ericson, published by Morgan Kaufmann Publishers, © 2005 Elsevier Inc”
I'm having a bit of issue trying to get meshes I import into my program to have cloth simulation physics using a particle/spring system. I'm kind of a beginner into graphics programming, so sorry if this is super obvious and I'm just missing something. I'm using C++ with OpenGL, as well as Assimp to import the models. I'm fairly sure my code to calculate the constraints/springs and step each particle is correct, as I tested it out with generated meshes (with quads instead of triangles), and it looked fine, but idk.
I've been using this link to study up on how to actually do this: https://nccastaff.bournemouth.ac.uk/jmacey/MastersProjects/MSc2010/07LuisPereira/Thesis/LuisPereira_Thesis.pdf
What it looks like in-engine: https://www.youtube.com/watch?v=RyAan27wryU
I'm pretty sure it's an issue with the connections/springs, as the imported model thats just a flat plane seems to work fine, for the most part. The other model though.. seems to just fall apart. I keep looking at papers on this, and from what I understand everything should be working right, as I connect the edge/bend springs seemingly correctly, and the physics side seems to work from the flat planes. I really can't figure it out for the life of me! Any tips/help would be GREATLY appreciated! :)
Code for processing Mesh into Cloth:
// Container to temporarily hold faces while we process springs
std::vector<Face> faces;
// Go through indices and take the ones making a triangle.
// Indices come from assimp, so i think this is the right thing to do to get each face?
for (int i = 0; i < this->indices.size(); i+=3)
{
std::vector<unsigned int> faceIds = { this->indices.at(i), this->indices.at(i + 1), this->indices.at(i + 2) };
Face face;
face.vertexIDs = faceIds;
faces.push_back(face);
}
// Iterate through faces and add constraints when needed.
for (int l = 0; l < faces.size(); l++)
{
// Adding edge springs.
Face temp = faces[l];
makeConstraint(particles.at(temp.vertexIDs[0]), particles.at(temp.vertexIDs[1]));
makeConstraint(particles.at(temp.vertexIDs[0]), particles.at(temp.vertexIDs[2]));
makeConstraint(particles.at(temp.vertexIDs[1]), particles.at(temp.vertexIDs[2]));
// We need to get the bending springs as well, and i've just written a function to do that.
for (int x = 0; x < faces.size(); x++)
{
Face temp2 = faces[x];
if (l != x)
{
verticesShared(temp, temp2);
}
}
}
And heres the code where I process the bending springs as well:
// Container for any indices the two faces have in common.
std::vector<glm::vec2> traversed;
// Loop through both face's indices, to see if they match eachother.
for (int i = 0; i < a.vertexIDs.size(); i++)
{
for (int k = 0; k < b.vertexIDs.size(); k++)
{
// If we do get a match, we push a vector into the container containing the two indices of the faces so we know which ones are equal.
if (a.vertexIDs.at(i) == b.vertexIDs.at(k))
{
traversed.push_back(glm::vec2(i, k));
}
}
// If we're here, if means we have an edge in common, aka that we have two vertices shared between the two faces.
if (traversed.size() == 2)
{
// Get the adjacent vertices.
int face_a_adj_ind = 3 - ((traversed[0].x) + (traversed[1].x));
int face_b_adj_ind = 3 - ((traversed[0].y) + (traversed[1].y));
// Turn the stored ones from earlier and just get the ACTUAL indices from the face. Indices of indices, eh.
unsigned int adj_1 = a.vertexIDs[face_a_adj_ind];
unsigned int adj_2 = b.vertexIDs[face_b_adj_ind];
// And finally, make a bending spring between the two adjacent particles.
makeConstraint(particles.at(adj_1), particles.at(adj_2));
}
}
I am using cocos2d-x 3.8.
I try to create two polygon sprites with the following code.
I know we can detect intersect with BoundingBox but is too rough.
Also, I know we can use Cocos2d-x C++ Physics engine to detect collisions but doesn't it waste a lot of resource of the mobile device? The game I am developing does not need physics engine.
is there a way to detect the intersect of polygon sprites?
Thank you.
auto pinfoTree = AutoPolygon::generatePolygon("Tree.png");
auto treeSprite= Sprite::create(pinfoTree);
treeSprite-> setPosition(width / 4 * 3 - 30 , height / 2 - 200);
this->addChild(treeSprite);
auto pinfoBird = AutoPolygon::generatePolygon("Bird.png");
auto Bird= Sprite::create(pinfoTree);
Bird->setPosition(width / 4 * 3, height / 2);
this->addChild(Bird)
This is a bit more complicated: AutoPolygon gives you a bunch of triangles - the PhysicsBody::createPolygon requires a convex polygon with clockwise winding… so these are 2 different things. The vertex count might even be limited. I think Box2d’s maximum count for 1 polygon is 8.
If you want to try this you’ll have to merge the triangles to form polygons. An option would be to start with one triangle and add more as long as the whole thing stays convex. If you can’t add any more triangles start a new polygon. Add all the polygons as PhysicsShapes to your physics body to form a compound object.
I would propose that you don’t follow this path because
Autopolygon is optimized for rendering - not for best fitting
physics - that is a difference. A polygon traced with Autopolygon will always be bigger than the original sprite - Otherwise you would see rendering artifacts.
You have close to no control over the generated polygons
Tracing the shape in the app will increase your startup time
Triangle meshes and physics outlines are 2 different things
I would try some different approach: Generate the collision shapes offline. This gives you a bunch of advantages:
You can generate and tweak the polygons in a visual editor e.g. by
using PhysicsEditor
Loading the prepares polygons is way faster
You can set additional parameters like mass etc
The solution is battle proven and works out of the box
But if you want to know how polygon intersect work. You can look at this code.
// Calculate the projection of a polygon on an axis
// and returns it as a [min, max] interval
public void ProjectPolygon(Vector axis, Polygon polygon, ref float min, ref float max) {
// To project a point on an axis use the dot product
float dotProduct = axis.DotProduct(polygon.Points[0]);
min = dotProduct;
max = dotProduct;
for (int i = 0; i < polygon.Points.Count; i++) {
flaot d = polygon.Points[i].DotProduct(axis);
if (d < min) {
min = dotProduct;
} else {
if (dotProduct> max) {
max = dotProduct;
}
}
}
}
// Calculate the distance between [minA, maxA] and [minB, maxB]
// The distance will be negative if the intervals overlap
public float IntervalDistance(float minA, float maxA, float minB, float maxB) {
if (minA < minB) {
return minB - maxA;
} else {
return minA - maxB;
}
}
// Check if polygon A is going to collide with polygon B.
public boolean PolygonCollision(Polygon polygonA, Polygon polygonB) {
boolean result = true;
int edgeCountA = polygonA.Edges.Count;
int edgeCountB = polygonB.Edges.Count;
float minIntervalDistance = float.PositiveInfinity;
Vector edge;
// Loop through all the edges of both polygons
for (int edgeIndex = 0; edgeIndex < edgeCountA + edgeCountB; edgeIndex++) {
if (edgeIndex < edgeCountA) {
edge = polygonA.Edges[edgeIndex];
} else {
edge = polygonB.Edges[edgeIndex - edgeCountA];
}
// ===== Find if the polygons are currently intersecting =====
// Find the axis perpendicular to the current edge
Vector axis = new Vector(-edge.Y, edge.X);
axis.Normalize();
// Find the projection of the polygon on the current axis
float minA = 0; float minB = 0; float maxA = 0; float maxB = 0;
ProjectPolygon(axis, polygonA, ref minA, ref maxA);
ProjectPolygon(axis, polygonB, ref minB, ref maxB);
// Check if the polygon projections are currentlty intersecting
if (IntervalDistance(minA, maxA, minB, maxB) > 0)
result = false;
return result;
}
}
The function can be used this way
boolean result = PolygonCollision(polygonA, polygonB);
I once had to program a collision detection algorithm where a ball was to collide with a rotating polygon obstacle. In my case the obstacles where arcs with certain thickness. and where moving around an origin. Basically it was rotating in an orbit. The ball was also rotating around an orbit about the same origin. It can move between orbits. To check the collision I had to just check if the balls angle with respect to the origin was between the lower and upper bound angles of the arc obstacle and check if the ball and the obstacle where in the same orbit.
In other words I used the various constrains and properties of the objects involved in the collision to make it more efficient. So use properties of your objects to cause the collision. Try using a similar approach depending on your objects
I am really new to OpenGL and I am trying to just make a surface from two triangles. I don't know where I am going wrong with this code. I know that all the positions and colors are getting into the triangles class and that the Triangles are being made, but it's not getting outputted. Can someone help?
I tried to get just the output from the Triangle class but it doesn't seem to be working. I don't think there's anything wrong with the way I am calling the Display function.
Code:
#include<GL/gl.h>
#include<GL/glu.h>
#include<GL/glut.h>
#include<iostream>
#include<vector>
using namespace std;
class Triangle
{
public:
float position[9],color[3];
Triangle()
{}
Triangle(float position_t[], float color_t[])
{
for(int i=0;i<9;i++)
{position[i] = position_t[i];}
for(int i=0;i<3;i++)
{color[i]= color_t[i];}
}
void makeTriangle()
{
glBegin(GL_TRIANGLES);
glColor3f(color[0],color[1],color[2]);glVertex3f(position[0],position[1],position[2]);
glColor3f(color[0],color[1],color[2]);glVertex3f(position[3],position[4],position[5]);
glColor3f(color[0],color[1],color[2]);glVertex3f(position[6],position[7],position[8]);
glEnd();}
};
class Mesh
{
public:
/*float center[3],position[9],color[3];
float size;*/
vector<Triangle> elements;
float center[3],position[9],color[3];
float size;
Mesh(){}
Mesh(float center_in[3], float color_in[3])
{
for (int i=0;i<3;i++)
{
color[i] = color_in[i];
center[i] = center_in[i];
}
}
void getPositions()
{
position[0] = 1;position[1] = 1; position[2] = 1;
position[3] = -1;position[4] = -1; position[5] = 1;
position[6] = 1;position[7] = -1; position[8] = 1;
}
void getColor()
{
color[0] = 1; color[1]=0; color[2]=0;
}
static Mesh makeMesh()
{
Mesh a;
a.elements.resize(2);
a.getPositions();
a.getColor();
Triangle T(a.position,a.color);
a.elements[0] = T;
//Triangle O(2);
//a.elements[1] = 0;
return a;
}
};
void render()
{
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
Mesh a;
a.elements.resize(2);
a.getPositions();
a.getColor();
Triangle T(a.position,a.color);
//vector<Mesh> m;
//m.push_back(Mesh::makeMesh());
glPushMatrix();
T.makeTriangle();
glPopMatrix();
glFlush();
glutSwapBuffers();
glutPostRedisplay();
}
Full Code: http://pastebin.com/xa3B7166
As I suggested you in the comments, you are not setting the gluLookat() function. Everything is being drawn but you are just not looking at it!
Docs: https://www.opengl.org/sdk/docs/man2/xhtml/gluLookAt.xml
Your code does not specify any transformations. Therefore, your coordinates need to be within the default view volume, which is [-1, 1] in all coordinate directions.
Or more technically, the model/view/projection transformations (or all the transformations applied in your vertex shader if you use the programmable pipeline) transform the coordinates into the clip coordinate space, and after perspective division into the normalized device coordinate (aka NDC) space. The range of the NDC space is [-1, 1] for all coordinates.
If you don't apply any transformations, like is the case in your code, your original coordinates already have to be in NDC space.
With your current coordinates:
position[0] = 1;position[1] = 1; position[2] = 1;
position[3] = -1;position[4] = -1; position[5] = 1;
position[6] = 1;position[7] = -1; position[8] = 1;
all the z-coordinates have values of 1, which means that the whole triangle is right on the boundary of the clip volume. To make it visible, you can simply set the z-coordinates to 0:
position[0] = 1;position[1] = 1; position[2] = 0;
position[3] = -1;position[4] = -1; position[5] = 0;
position[6] = 1;position[7] = -1; position[8] = 0;
This centers it within the NDC space in z-direction, with the vertices being on 3 of the corners in the xy-plane. You will therefore see half of your window covered by the triangle, cutting it in half along the diagonal.
It's of course common in OpenGL to have the original coordinates in a different coordinate space, and then apply transformations to place them within the view volume.
You're probably already aware of this, but I thought I'd mention it anyway: If you're just starting to learn OpenGL, I would suggest that you learn what people often call "modern OpenGL". This includes the OpenGL Core Profile, or OpenGL ES 2.0 or later. The calls you are using now are mostly deprecated in newer versions of OpenGL, and not available anymore in the Core Profile and ES. The initial hurdle is somewhat higher for "modern OpenGL", particularly since you have to write your own shaders, but you will get on the path to acquiring knowledge that is still current.