OpenGL Shader stretches geomatry - c++

I created a simple program that renders a quad
Initialize:
Math::float3 vertices[4];
vertices[0] = Math::float3(-0.5f, 0.5f, -1.0f);
vertices[1] = Math::float3(-0.5f, -0.5f, -1.0f);
vertices[2] = Math::float3(0.5f, -0.5f, -1.0f);
vertices[3] = Math::float3(0.5f, 0.5f, -1.0f);
glGenBuffers(1, &VBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
unsigned int indices[] = {
0, 1, 2,
2, 3, 0
};
glGenBuffers(1, &IBO);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
Rendering:
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glVertexAttribPointer(0, 3, GL_FLOAT, false, sizeof(Math::float3), 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IBO);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
glDisableVertexAttribArray(0);
Which renders a perfectly square quad.
I continued by adding a vertex shader program:
Vertex shader
layout (location = 0) in vec3 Position;
void main(){
gl_Position = vec4(Position.x, Position.y, Position.z, 1.0);
}
Fragment shader
out vec4 FragColor;
void main()
{
FragColor = vec4(1.0, 0.0, 0.0, 1.0);
}
And if I run my program again, the quad seems to be stretched to about twice its size on x axis, and stretched slightly on the Y.
Without shaders
With shaders
Any idea on what could be causing this? If you need more code snippets or additional info, please let me know :)
Update
Some extra code.
Opening the window / reshape
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
glutInitWindowPosition(0, 0);
glutInitWindowSize(SCREEN_WIDTH, SCREEN_HEIGHT);
glutCreateWindow(TITLE);
...
if(_h == 0) _h = 1;
float ratio = 1.0f * _w / _h;
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glViewport(0, 0, _w, _h);
gluPerspective(45.0f, ratio, 1, 1000);
glMatrixMode(GL_MODELVIEW);
Update 2
My problem sadly still persists, some extra info here:
My geomatry:
Math::float3 vertices[4];
vertices[0] = Math::float3(-0.5, -0.5f, -1.0f);
vertices[1] = Math::float3(0.5f, -0.5f, -1.0f);
vertices[2] = Math::float3(0.5f, 0.5f, -1.0f);
vertices[3] = Math::float3(-0.5f, 0.5f, -1.0f);
unsigned int indices[] = { 0, 1, 2, 2, 3, 0 };
My vertex shader
#version 330
layout (location = 0) in vec3 Position;
uniform mat4 MVP;
void main()
{
gl_Position = MVP * vec4(Position.x, Position.y, Position.z, 1.0);
}
Setup view
#define SCREEN_WIDTH 800
#define SCREEN_HEIGHT 600
#define FOV 60.0f
#define RATIO 1.0f * SCREEN_WIDTH / SCREEN_HEIGHT
#define ZNEAR 1.0f
#define ZFAR 1000.0f
if(_h == 0) _h = 1;
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glViewport(0, 0, _w, _h);
gluPerspective(FOV, RATIO, ZNEAR, ZFAR);
glMatrixMode(GL_MODELVIEW);
Initialize
Math::float3 vertices[4];
vertices[0] = Math::float3(-0.5, -0.5f, -1.0f);
vertices[1] = Math::float3(0.5f, -0.5f, -1.0f);
vertices[2] = Math::float3(0.5f, 0.5f, -1.0f);
vertices[3] = Math::float3(-0.5f, 0.5f, -1.0f);
glGenBuffers(1, &VBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
unsigned int indices[] = { 0, 1, 2, 2, 3, 0 };
glGenBuffers(1, &IBO);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IBO);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
sl = new Loader::ShaderLoader();
sl->Initialize();
sl->AddShader("data/shaders/shader.vs", VERTEX_SHADER);
sl->AddShader("data/shaders/shader.fs", FRAGMENT_SHADER);
sl->CompileShaders();
Render
MVP = glGetUniformLocation(sl->GetShaderProgram(), "MVP");
float m[16];
f -= 0.01f;
m[0] = 1.0f;
m[1] = 0.0f;
m[2] = 0.0f;
m[3] = 0.0f;
m[4] = 0.0f;
m[5] = 1.0f;
m[6] = 0.0f;
m[7] = 0.0f;
m[8] = 0.0f;
m[9] = 0.0f;
m[10] = 1.0f;
m[11] = 0.0f;
m[12] = 0.0f;
m[13] = 0.0f;
m[14] = 0.0f;
m[15] = 1.0f;
glUniformMatrix4fv(MVP, 1, GL_TRUE, m);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glVertexAttribPointer(0, 3, GL_FLOAT, false, 0, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, IBO);
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
glDisableVertexAttribArray(0);
I've also printed the value for MVP per render call, and it's always 0 for some reason.
Again, any additional tips are welcome, thanks!

Most likely you have a non-identity transformation chain (non-identity projection and/or modelview matrix) set up with the fixed function. When using shaders the fixed function matrices are not used, which may explain the difference.

This is caused by different approach to PVM (projection-view-model) matrix in OpenGL. In fixed pipeline, this matrix was defined by functions glMatrixMode.
When shaders are used, these matrices are usually sent to vertex shader as uniform and handled here.
Your vertex shader then will be something like this:
in vec3 Position;
uniform mat4 Projection;
uniform mat4 View;
uniform mat4 Model;
void main(){
gl_Position = Projection * View * Model * vec4(Position.x, Position.y, Position.z, 1.0);
}
This should provide some more info about these three matrices: Tutorial 3 matrices

Related

Rotate camera around z axis by 45 degrees works but not around x axis

I'm trying to setup an orthographic camera in C++ and I have some problems getting the rotation correctly.
When I try to rotate the camera around the z axis by 45 degrees, everything works as expected (model is defined from -0.5f to 0.5f).
However, when trying to rotate around x axis, the angle gets really amplified (i.e. rotation around 1 radian makes it almost disappear).
Here is the related code:
int main(int argc, char** argv)
{
sdl2::Context context;
sdl2::Window window("myWindow", 800, 600);
sdl2::GLContext glContext(window);
//make the shader
Shader shader("shaders/quad.vert", "shaders/quad.frag");
Quad quad;
//create a orthographic projection
glm::mat4 projection = glm::ortho(0.0f, 800.0f, 0.0f, 600.0f);
auto zAxis = glm::vec3(0.0f, 0.0f, 1.0f);
glUseProgram(shader.getID());
auto projectionLoc = glGetUniformLocation(shader.getID(), "projection");
glUniformMatrix4fv(projectionLoc, 1, false, glm::value_ptr(projection));
auto viewLoc = glGetUniformLocation(shader.getID(), "view");
auto viewTransform = glm::mat4(1.0f);
auto zRot = glm::quat(glm::vec3(glm::radians(1.0f), glm::radians(0.0f), glm::radians(0.0f)));
viewTransform *= glm::toMat4(zRot);
glUniformMatrix4fv(viewLoc, 1, true, glm::value_ptr(viewTransform));
bool quit = false;
SDL_Event e;
while (!quit)
{
while (SDL_PollEvent(&e) != 0)
{
if (e.type == SDL_QUIT)
{
quit = true;
}
}
glClear(GL_COLOR_BUFFER_BIT);
quad.render(shader);
SDL_GL_SwapWindow(window());
}
SDL_Delay(3000);
return 0;
}
#version 430 core
layout (location = 0) in vec3 pos;
layout (location = 1) in vec2 uv;
uniform mat4 projection;
uniform mat4 view;
uniform mat4 model;
void main()
{
gl_Position = projection * view * model * vec4(pos, 1.0);
}
Quad::Quad() :
_position(0, 0, 0)
{
glCreateBuffers(1, &_vbo);
glCreateVertexArrays(1, &_vao);
glGenBuffers(1, &_ebo);
float vertices[] = {
0.5f, 0.5f, 0.0f, // top right
0.5f, -0.5f, 0.0f, // bottom right
-0.5f, -0.5f, 0.0f, // bottom left
-0.5f, 0.5f, 0.0f // top left
};
uint32_t indices[] = {
0, 1, 3,
1, 2, 3
};
glBindVertexArray(_vao);
glBindBuffer(GL_ARRAY_BUFFER, _vbo);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, _ebo);
glEnableVertexAttribArray(0);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(indices), indices, GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(float), (void*)0);
}
Quad::~Quad()
{
glDeleteVertexArrays(1, &_vao);
glDeleteBuffers(1, &_vbo);
}
void Quad::render(const Shader& shader)
{
glBindVertexArray(_vao);
glUseProgram(shader.getID());
auto modelView = glm::mat4(1.0f);
//modelView = glm::translate(modelView, glm::vec3(400.0f, 300.0f, 0.0f));
modelView = glm::scale(modelView, glm::vec3(400.0f, 400.0f, 1.0f));
//modelView = glm::scale(modelView, glm::vec3(800, 600, 0));
auto modelLoc = glGetUniformLocation(shader.getID(), "model");
auto viewLoc = glGetUniformLocation(shader.getID(), "view");
auto projectionLoc = glGetUniformLocation(shader.getID(), "projection");
glUniformMatrix4fv(modelLoc, 1, false, glm::value_ptr(modelView));
glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, 0);
}
When you rotate a round the x or y axis, then the objects is clipped by the near and far plane of the Orthographic projection. By default near is -1.0 and far is 1.0. Increase the distance to the near and far plane (see glm::ortho). For instance:
glm::mat4 projection = glm::ortho(0.0f, 800.0f, 0.0f, 600.0f);
glm::mat4 projection = glm::ortho(0.0f, 800.0f, 0.0f, 600.0f, -500.0f, 500.0f);

Strange MVP behavior during translation

I'm learning the basics of OpenGL and trying to translate a triangle with ortho projection. I don't see what I expect, what am I doing wrong?
My Vertex buffer:
Vertices[0] = Vector3f(-1.0f, -1.0f, 0.0f);
Vertices[1] = Vector3f(1.0f, -1.0f, 0.0f);
Vertices[2] = Vector3f(-1.0f, 1.0f, 0.0f);
glGenBuffers(1, &VBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(Vertices), Vertices, GL_STATIC_DRAW);
Vertex shader:
#version 330
layout (location = 0) in vec3 Position;
uniform mat4 gMVP;
void main()
{
gl_Position = gMVP * vec4(Position, 1.0);
}
MVP calculation and rendering:
glm::mat4 p = glm::ortho(-2.0f, 2.0f, -2.0f, 2.0f, -2.0f, 2.0f);
glm::mat4 v = glm::lookAt(glm::vec3(0,0,1), glm::vec3(0,0,0), glm::vec3(0,1,0));
glm::mat4 m = glm::translate(glm::mat4(1.0f), glm::vec3(0.5f, 0.0f, 0.0f));
glm::mat4 MVP = p * v * m;
glUniformMatrix4fv(gMVPLocation, 1, GL_TRUE, &MVP[0][0]);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
glDrawArrays(GL_TRIANGLES, 0, 3);
glDisableVertexAttribArray(0);
glutSwapBuffers();
the result:
Shouldn't it just move to the right along the X axis?
The 3rd parameter of glUniformMatrix4fv causes that the matrix will be transposed when it is set to the uniform. OpenGL Mathematics (GLM) constructs the matrices in the same way, as GLSL constructs variables of type mat4.
The matrix has not to be transposed when it is set to the uniform:
glUniformMatrix4fv(gMVPLocation, 1, GL_TRUE, &MVP[0][0]);
glUniformMatrix4fv(gMVPLocation, 1, GL_FALSE, &MVP[0][0]);
In GLSL the vector has to be multiplied to the matrix from the right. See GLSL Programming/Vector and Matrix Operations

How to draw multiple objects in OpenGL using multiple VAO and VBO?

I'm trying to render multiple objects in OpenGL using multiple VAO's and VBO's. To render multiple objects using the same vertices I've done it, but what I want to do is to use different vertices for each object, for example to draw a square and a circle. For a square I only need 6 vertices but for circle I need 360.
I have error with reading or creating the shaders.
Here is the Vertex Shader:
#version 330 core
layout (location = 0) in vec4 position;
uniform mat4 model;
uniform mat4 view;
uniform mat4 projection;
void main()
{
gl_Position = projection * view * model * position;
}
Fragment Shader:
#version 330 core
layout(location = 0) out vec4 color;
uniform vec4 u_Color;
void main()
{
color = u_Color;
}
The VAO and VBO generating and binding
// Circle
std::vector<VertexFormat> vertices;
for (int i = 0; i < 360; i++)
{
GLfloat angle = i * ((2.0f * 3.14159f) / 360);
vertices.push_back(VertexFormat(glm::vec3(cos(angle) * 100.0f, sin(angle) * 100.0f, 0.0f)));
}
// Pipette object
std::vector<VertexFormat> pipetteVertices;
pipetteVertices.push_back(VertexFormat(glm::vec3(injPipette.x + 500.0f, injPipette.y + 500.0f, 0.0f))); // 0
pipetteVertices.push_back(VertexFormat(glm::vec3(injPipette.x + 700.0f, injPipette.y + 500.0f, 0.0f))); // 1
pipetteVertices.push_back(VertexFormat(glm::vec3(injPipette.x + 700.0f, injPipette.y + 700.0f, 0.0f))); // 2
pipetteVertices.push_back(VertexFormat(glm::vec3(injPipette.x + 500.0f, injPipette.y + 700.0f, 0.0f))); // 3
pipetteVertices.push_back(VertexFormat(glm::vec3(injPipette.x + 500.0f, injPipette.y + 500.0f, 0.0f)));
pipetteVertices.push_back(VertexFormat(glm::vec3(injPipette.x + 700.0f, injPipette.y + 700.0f, 0.0f)));
GLuint vao;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
GLuint vbo;
glGenBuffers(1, &vbo);
glBindBuffer(GL_ARRAY_BUFFER, vbo);
glBufferData(GL_ARRAY_BUFFER, sizeof(VertexFormat) * 6, &pipetteVertices[0], GL_STATIC_DRAW);
//Position attribute
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(VertexFormat), (GLvoid *)0);
GLuint vao2;
glGenVertexArrays(1, &vao2);
glBindVertexArray(vao2);
GLuint vbo2;
glGenBuffers(1, &vbo2);
glBindBuffer(GL_ARRAY_BUFFER, vbo2);
glBufferData(GL_ARRAY_BUFFER, sizeof(VertexFormat) * 360, &vertices[0], GL_STATIC_DRAW);
//Position attribute
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, sizeof(VertexFormat), (GLvoid *) 0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
And the draw call in the rendering loop:
//Get the uniform locations of model, view and projection matrices
modelID = glGetUniformLocation(program, "model");
viewID = glGetUniformLocation(program, "view");
projectionID = glGetUniformLocation(program, "projection");
//View transform
glm::mat4 view = glm::lookAt(glm::vec3(0, 0, 2), glm::vec3(0, 0, 0), glm::vec3(0, 1, 0));
//Projection transform
//glm::mat4 projection = glm::perspective(45.0f, (GLfloat)screenWidth / (GLfloat)screenHeight, 0.1f, 1000.0f);
glm::mat4 projection = glm::ortho(0.0f, (GLfloat)screenWidth, 0.0f, (GLfloat)screenHeight, 0.1f, 10.0f);
{
glUniformMatrix4fv(viewID, 1, GL_FALSE, glm::value_ptr(view));
glUniformMatrix4fv(projectionID, 1, GL_FALSE, glm::value_ptr(projection));
glm::mat4 translate = glm::translate(glm::mat4(1.0), glm::vec3(100.0f + move_x, 100.0f + move_y, 0.0f));
glm::mat4 rotate = glm::rotate(glm::mat4(1.0), 0.0f, glm::vec3(0.0f, 0.0f, 1.0f));
glm::mat4 scale = glm::scale(glm::mat4(1.0), glm::vec3(1.0f, 1.0f, 2.0f));
glm::mat4 model = translate * rotate * scale;
glUniformMatrix4fv(modelID, 1, GL_FALSE, glm::value_ptr(model));
glUniform4f(color, 0.0f, 0.0f, 1.0f, 1.0f);
//Render
glDrawArrays(GL_TRIANGLE_FAN, 0, 360);
}
{
glUniformMatrix4fv(viewID, 1, GL_FALSE, glm::value_ptr(view));
glUniformMatrix4fv(projectionID, 1, GL_FALSE, glm::value_ptr(projection));
glm::mat4 translate = glm::translate(glm::mat4(1.0), glm::vec3(300.0f + injPipette.x, 300.0f + injPipette.y, 0.0f));
glm::mat4 rotate = glm::rotate(glm::mat4(1.0), 0.0f, glm::vec3(0.0f, 0.0f, 1.0f));
glm::mat4 scale = glm::scale(glm::mat4(1.0), glm::vec3(1.0f, 1.0f, 2.0f));
glm::mat4 model = translate * rotate * scale;
glUniformMatrix4fv(modelID, 1, GL_FALSE, glm::value_ptr(model));
glUniform4f(color, 1.0f, 0.0f, 0.0f, 0.5f);
//Render
glDrawArrays(GL_TRIANGLES, 0, 6);
}
I repeat, to draw multiple objects using the same vertices I've done it. I need to know how to draw multiple objects using the same vertex and fragment shader but different number of vertices. The project is small, just rendering maximum 10 objects in 2D.
Drawing commands such as glDrawArrays process and draw the arrays of generic vertex attribute data specified in the currently bound Vertex Array Object.
This means that you need to bind the correct vertex array object before executing the Draw call:
// [...]
glBindVertexArray(vao2);
glDrawArrays(GL_TRIANGLE_FAN, 0, 360);
// [...]
glBindVertexArray(vao);
glDrawArrays(GL_TRIANGLES, 0, 6);
I found a project with the code:
#pragma once
#include "glm\glm.hpp"
struct VertexFormat
{
glm::vec3 position;
VertexFormat(const glm::vec3 &iPos)
{
position = iPos;
}
VertexFormat()
{
}
};

Dashed line in OpenGL3?

I'm currently porting an old OpenGL 1.1 application which makes use of wireframe models to OpenGL 3.0.
In 1.1 following code is used to create a dashed line:
glPushAttrib(GL_ENABLE_BIT);
glLineStipple(1, 0x0F0F);
glEnable(GL_LINE_STIPPLE);
Here as usual the parameters are pushed to the stack in order to influence all following drawing operations.
My question: how is this done in OpenGL3 where this stack is no longer used? How can I set up my lines to be dashed (probably before handing the coordinates over to glBufferData()?
For separate line segments, this is not very complicated at all. For example drawing the GL_LINES primitives.
The trick is to know the start of the line segment in the fragment shader. This is quite simple by using the flat interpolation qualifier.
The vertex shader has to pass the normalized device coordinate to the fragment shader. Once with default interpolation and once with no (flat) interpolation. This causes that in the fragment shade, the first input parameter contains the NDC coordinate of the actual position on the line and the later the NDC coordinate of the start of the line.
#version 330
layout (location = 0) in vec3 inPos;
flat out vec3 startPos;
out vec3 vertPos;
uniform mat4 u_mvp;
void main()
{
vec4 pos = u_mvp * vec4(inPos, 1.0);
gl_Position = pos;
vertPos = pos.xyz / pos.w;
startPos = vertPos;
}
Additionally to the varying inputs, the fragment shader has uniform variables. u_resolution contains the width and the height of the viewport. u_dashSize contains the length of the line and u_gapSize the length of a gap in pixel.
So the length of the line from the start to the actual fragment can be calculated:
vec2 dir = (vertPos.xy-startPos.xy) * u_resolution/2.0;
float dist = length(dir);
And fragments on the gap can be discarded, by the discard command.
if (fract(dist / (u_dashSize + u_gapSize)) > u_dashSize/(u_dashSize + u_gapSize))
discard;
Fragment shader:
#version 330
flat in vec3 startPos;
in vec3 vertPos;
out vec4 fragColor;
uniform vec2 u_resolution;
uniform float u_dashSize;
uniform float u_gapSize;
void main()
{
vec2 dir = (vertPos.xy-startPos.xy) * u_resolution/2.0;
float dist = length(dir);
if (fract(dist / (u_dashSize + u_gapSize)) > u_dashSize/(u_dashSize + u_gapSize))
discard;
fragColor = vec4(1.0);
}
For the following simple demo program I've used the GLFW API for creating a window, GLEW for loading OpenGL and GLM -OpenGL Mathematics for the math. I don't provide the code for the function CreateProgram, which just creates a program object, from the vertex shader and fragment shader source code:
#include <GL/glew.h>
#include <GL/gl.h>
#include <glm/glm.hpp>
#include <glm/gtc/matrix_transform.hpp>
#include <glm/gtc/type_ptr.hpp>
#include <GLFW/glfw3.h>
#include <vector>
#define _USE_MATH_DEFINES
#include <math.h>
int main(void)
{
if (glfwInit() == GLFW_FALSE)
return 0;
GLFWwindow *window = glfwCreateWindow(400, 300, "OGL window", nullptr, nullptr);
if (window == nullptr)
return 0;
glfwMakeContextCurrent(window);
glewExperimental = true;
if (glewInit() != GLEW_OK)
return 0;
GLuint program = CreateProgram(vertShader, fragShader);
GLint loc_mvp = glGetUniformLocation(program, "u_mvp");
GLint loc_res = glGetUniformLocation(program, "u_resolution");
GLint loc_dash = glGetUniformLocation(program, "u_dashSize");
GLint loc_gap = glGetUniformLocation(program, "u_gapSize");
glUseProgram(program);
glUniform1f(loc_dash, 10.0f);
glUniform1f(loc_gap, 10.0f);
std::vector<float> varray{
-1, -1, -1, 1, -1, -1, 1, 1, -1, -1, 1, -1,
-1, -1, 1, 1, -1, 1, 1, 1, 1, -1, 1, 1
};
std::vector<unsigned int> iarray{
0, 1, 1, 2, 2, 3, 3, 0,
4, 5, 5, 6, 6, 7, 7, 4,
0, 4, 1, 5, 2, 6, 3, 7
};
GLuint bo[2], vao;
glGenBuffers(2, bo);
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glEnableVertexAttribArray(0);
glBindBuffer(GL_ARRAY_BUFFER, bo[0] );
glBufferData(GL_ARRAY_BUFFER, varray.size()*sizeof(*varray.data()), varray.data(), GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, bo[1]);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, iarray.size()*sizeof(*iarray.data()), iarray.data(), GL_STATIC_DRAW);
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glm::mat4 view = glm::lookAt(glm::vec3(0.0f, 0.0f, 5.0f), glm::vec3(0.0f, 0.0f, 0.0f), glm::vec3(0.0f, 1.0f, 0.0f));
glm::mat4 project;
int vpSize[2]{0, 0};
while (!glfwWindowShouldClose(window))
{
int w, h;
glfwGetFramebufferSize(window, &w, &h);
if (w != vpSize[0] || h != vpSize[1])
{
vpSize[0] = w; vpSize[1] = h;
glViewport(0, 0, vpSize[0], vpSize[1]);
project = glm::perspective(glm::radians(90.0f), (float)w/(float)h, 0.1f, 10.0f);
glUniform2f(loc_res, (float)w, (float)h);
}
static float angle = 1.0f;
glm::mat4 modelview( 1.0f );
modelview = glm::translate(modelview, glm::vec3(0.0f, 0.0f, -3.0f) );
modelview = glm::rotate(modelview, glm::radians(angle), glm::vec3(1.0f, 0.0f, 0.0f));
modelview = glm::rotate(modelview, glm::radians(angle*0.5f), glm::vec3(0.0f, 1.0f, 0.0f));
angle += 0.5f;
glm::mat4 mvp = project * modelview;
glUniformMatrix4fv(loc_mvp, 1, GL_FALSE, glm::value_ptr(mvp));
glClear(GL_COLOR_BUFFER_BIT);
glDrawElements(GL_LINES, (GLsizei)iarray.size(), GL_UNSIGNED_INT, nullptr);
glfwSwapBuffers(window);
glfwPollEvents();
}
glfwTerminate();
return 0;
}
Things get a bit more complicated, if the goal is to draw a dashed line along a polygon. For example drawing a GL_LINE_STRIP primitive.
The length of the line cannot be calculated in the shader program, without knowing all the primitives of the line. Even if all the primitives would be known (e.g. SSBO), then the calculation would have to be done in a loop.
I decided to add an additional attribute to the shader program, which contains the "distance" from the start of the line to the vertex coordinate. By "distance" is meant the length of the projected polygon on to the viewport.
This causes that the vertex shader and fragment shader is even simpler:
Vertex shader:
#version 330
layout (location = 0) in vec3 inPos;
layout (location = 1) in float inDist;
out float dist;
uniform mat4 u_mvp;
void main()
{
dist = inDist;
gl_Position = u_mvp * vec4(inPos, 1.0);
}
Fragment shader:
#version 330
in float dist;
out vec4 fragColor;
uniform vec2 u_resolution;
uniform float u_dashSize;
uniform float u_gapSize;
void main()
{
if (fract(dist / (u_dashSize + u_gapSize)) > u_dashSize/(u_dashSize + u_gapSize))
discard;
fragColor = vec4(1.0);
}
In the demo program the inDist attribute is calculated on the CPU. Each vertex coordinate is transformed by the model, view, projection matrix. Finally it is transformed from normalized device space to window space. The XY distance between adjacent coordinates of the line strip is calculated and the lengths are summed along the line strip and assigned to the corresponding attribute value:
int w = [...], h = [...]; // window widht and height
glm::mat4 mpv = [...]; // model view projection matrix
std::vector<glm::vec3> varray{ [...] }; // array of vertex
std::vector<float> darray(varray.size(), 0.0f); // distance attribute - has to be computed
glm::mat4 wndmat = glm::scale(glm::mat4(1.0f), glm::vec3((float)w/2.0f, (float)h/2.0f, 1.0f));
wndmat = glm::translate(wndmat, glm::vec3(1.0f, 1.0f, 0.0f));
glm::vec2 vpPt(0.0f, 0.0f);
float dist = 0.0f;
for (size_t i=0; i < varray.size(); ++i)
{
darray[i] = dist;
glm::vec4 clip = mvp * glm::vec4(varray[i], 1.0f);
glm::vec4 ndc = clip / clip.w;
glm::vec4 vpC = wndmat * ndc;
float len = i==0 ? 0.0f : glm::length(vpPt - glm::vec2(vpC));
vpPt = glm::vec2(vpC);
dist += len;
}
Demo program:
int main(void)
{
if (glfwInit() == GLFW_FALSE)
return 0;
GLFWwindow *window = glfwCreateWindow(800, 600, "OGL window", nullptr, nullptr);
if (window == nullptr)
return 0;
glfwMakeContextCurrent(window);
glewExperimental = true;
if (glewInit() != GLEW_OK)
return 0;
GLuint program = CreateProgram(vertShader, fragShader);
GLint loc_mvp = glGetUniformLocation(program, "u_mvp");
GLint loc_res = glGetUniformLocation(program, "u_resolution");
GLint loc_dash = glGetUniformLocation(program, "u_dashSize");
GLint loc_gap = glGetUniformLocation(program, "u_gapSize");
glUseProgram(program);
glUniform1f(loc_dash, 10.0f);
glUniform1f(loc_gap, 10.0f);
std::vector<glm::vec3> varray;
for (size_t u=0; u <= 360; ++u)
{
double a = u*M_PI/180.0;
double c = cos(a), s = sin(a);
varray.emplace_back(glm::vec3((float)c, (float)s, 0.0f));
}
std::vector<float> darray(varray.size(), 0.0f);
GLuint bo[2], vao;
glGenBuffers(2, bo);
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
glBindBuffer(GL_ARRAY_BUFFER, bo[0] );
glBufferData(GL_ARRAY_BUFFER, varray.size()*sizeof(*varray.data()), varray.data(), GL_STATIC_DRAW);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
glBindBuffer(GL_ARRAY_BUFFER, bo[1] );
glBufferData(GL_ARRAY_BUFFER, darray.size()*sizeof(*darray.data()), darray.data(), GL_STATIC_DRAW);
glVertexAttribPointer(1, 1, GL_FLOAT, GL_FALSE, 0, 0);
glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
glm::mat4 view = glm::lookAt(glm::vec3(0.0f, 0.0f, 5.0f), glm::vec3(0.0f, 0.0f, 0.0f), glm::vec3(0.0f, 1.0f, 0.0f));
glm::mat4 project, wndmat;
int vpSize[2]{0, 0};
while (!glfwWindowShouldClose(window))
{
int w, h;
glfwGetFramebufferSize(window, &w, &h);
if (w != vpSize[0] || h != vpSize[1])
{
vpSize[0] = w; vpSize[1] = h;
glViewport(0, 0, vpSize[0], vpSize[1]);
project = glm::perspective(glm::radians(90.0f), (float)w/(float)h, 0.1f, 10.0f);
glUniform2f(loc_res, (float)w, (float)h);
wndmat = glm::scale(glm::mat4(1.0f), glm::vec3((float)w/2.0f, (float)h/2.0f, 1.0f));
wndmat = glm::translate(wndmat, glm::vec3(1.0f, 1.0f, 0.0f));
}
static float angle = 1.0f;
glm::mat4 modelview( 1.0f );
modelview = glm::translate(modelview, glm::vec3(0.0f, 0.0f, -2.0f) );
modelview = glm::rotate(modelview, glm::radians(angle), glm::vec3(1.0f, 0.0f, 0.0f));
modelview = glm::rotate(modelview, glm::radians(angle*0.5f), glm::vec3(0.0f, 1.0f, 0.0f));
angle += 0.5f;
glm::mat4 mvp = project * modelview;
glm::vec2 vpPt(0.0f, 0.0f);
float dist = 0.0f;
for (size_t i=0; i < varray.size(); ++i)
{
darray[i] = dist;
glm::vec4 clip = mvp * glm::vec4(varray[i], 1.0f);
glm::vec4 ndc = clip / clip.w;
glm::vec4 vpC = wndmat * ndc;
float len = i==0 ? 0.0f : glm::length(vpPt - glm::vec2(vpC));
vpPt = glm::vec2(vpC);
dist += len;
}
glBufferSubData(GL_ARRAY_BUFFER, 0, darray.size()*sizeof(*darray.data()), darray.data());
glUniformMatrix4fv(loc_mvp, 1, GL_FALSE, glm::value_ptr(mvp));
glClear(GL_COLOR_BUFFER_BIT);
glDrawArrays(GL_LINE_STRIP, 0, (GLsizei)varray.size());
glfwSwapBuffers(window);
glfwPollEvents();
}
glfwTerminate();
return 0;
}
See also
glLineStipple deprecated in OpenGL 3.1
OpenGL ES - Dashed Lines

Cube is not rendering in OpenGL

I'm trying to write a basic OpenGL 3.3 program with shaders, buffers, etc. drawing a cube. The problem is that the cube is not drawn. Sorry for such an amout of code, but i feel like the error might be anywhere, because to me it all seems right: display function is looping, shaders are compiled, matrices are passed to shaders. I suspecting that something might be wrong with culling. Please take a look. Here is the code (I'm using freeglut, first init() is called, then display runs in a loop):
initialization code:
struct ProgramData
{
GLuint theProgram;
GLuint iModel;
GLuint iView;
GLuint iProjection;
};
ProgramData shaderProgram;
ProgramData LoadProgram(const std::string &strVertexShader,
const std::string &strFragmentShader)
{
std::vector<GLuint> shaderList;
shaderList.push_back(LoadShader(GL_VERTEX_SHADER, strVertexShader));
shaderList.push_back(LoadShader(GL_FRAGMENT_SHADER, strFragmentShader));
ProgramData data;
data.theProgram = CreateProgram(shaderList);
data.iModel = glGetUniformLocation(data.theProgram, "mModel");
data.iView = glGetUniformLocation(data.theProgram, "mView");
data.iProjection = glGetUniformLocation(data.theProgram, "mProjection");
return data;
}
float cube_vertices[] = {
-1.0f, -1.0f, 1.0f,
1.0f, -1.0f, 1.0f,
1.0f, 1.0f, 1.0f,
-1.0f, 1.0f, 1.0f,
-1.0f, -1.0f, -1.0f,
1.0f, -1.0f, -1.0f,
1.0f, 1.0f, -1.0f,
-1.0f, 1.0f, -1.0f,
GREEN_COLOR,
BLUE_COLOR,
RED_COLOR,
BROWN_COLOR,
GREEN_COLOR,
BLUE_COLOR,
RED_COLOR,
BROWN_COLOR,
};
GLubyte cube_elements[] = {
0,1,2, 2,3,0,
0,3,4, 4,5,0,
0,5,6, 6,1,0,
1,6,7, 7,2,1,
7,4,3, 3,2,7,
4,7,6, 6,5,4
};
void InitializeProgram()
{
//initialize vertex buffer
glGenBuffers(1, &vertex_buffer_obj);
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer_obj);
glBufferData(GL_ARRAY_BUFFER, sizeof(cube_vertices),
cube_vertices, GL_STATIC_DRAW);
glBindBuffer(GL_ARRAY_BUFFER, 0);
//initialize index buffer
glGenBuffers(1, &index_buffer_obj);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, index_buffer_obj);
glBufferData(GL_ELEMENT_ARRAY_BUFFER, sizeof(cube_elements),
cube_elements, GL_STATIC_DRAW);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0);
shaderProgram = LoadProgram("shader.vert", "shader.frag");
}
void init()
{
InitializeProgram();
int numberOfVertices = 8;
size_t color_data_offset = sizeof(float) * 3 * numberOfVertices;
glGenVertexArrays(1, &vao);
glBindVertexArray(vao);
glBindBuffer(GL_ARRAY_BUFFER, vertex_buffer_obj);
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, 0);
glVertexAttribPointer(1, 4, GL_FLOAT, GL_FALSE, 0,
(void*)color_data_offset);
glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, index_buffer_obj);
glBindVertexArray(0);
glEnable(GL_CULL_FACE);
glCullFace(GL_BACK);
glFrontFace(GL_CW);
glEnable(GL_DEPTH_TEST);
glDepthMask(GL_TRUE);
glDepthFunc(GL_LEQUAL);
glDepthRange(0.0f, 1.0f);
}
vertex shader:
#version 330
layout (location = 0) in vec3 inPosition;
layout (location = 1) in vec3 color;
uniform mat4 mProjection;
uniform mat4 mView;
uniform mat4 mModel;
smooth out vec3 theColor;
void main()
{
gl_Position = mProjection * mView * mModel * vec4(inPosition, 1);
theColor = color;
}
fragment shader:
#version 330
smooth in vec3 theColor;
out vec4 outputColor;
void main()
{
outputColor = vec4(theColor, 1);
}
draw code:
glm::vec3 cam_pos(3, 2, 3);
void display()
{
glClearColor(0.3f, 0.3f, 0.3f, 1.0f);
glClearDepth(1.0f);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glUseProgram(shaderProgram.theProgram);
glm::mat4 model_matrix = glm::translate(glm::vec3(0, 0, 0));
glm::mat4 view_matrix = glm::lookAt(cam_pos,
glm::vec3(0, 0, 0), glm::vec3(0, 0, 1));
glm::mat4 proj_matrix = glm::perspective(45.0f, 1.0f, 1.0f, 100.0f);
glUniformMatrix4fv(shaderProgram.iProjection, 1,
GL_FALSE, glm::value_ptr(proj_matrix));
glUniformMatrix4fv(shaderProgram.iView, 1,
GL_FALSE, glm::value_ptr(view_matrix));
glUniformMatrix4fv(shaderProgram.iModel, 1,
GL_FALSE, glm::value_ptr(model_matrix));
glBindVertexArray(vao);
int size; glGetBufferParameteriv(GL_ELEMENT_ARRAY_BUFFER,
GL_BUFFER_SIZE, &size);
glDrawElements(GL_TRIANGLES, size / sizeof(GLubyte), GL_UNSIGNED_SHORT, 0);
glBindVertexArray(0);
glUseProgram(0);
glutSwapBuffers();
glutPostRedisplay();
}
UPD: in init method when an offset for colors is calculated should be
sizeof(float) * 3 * numberOfVertices instead of
sizeof(GLubyte) * 3 * numberOfVertices, colors are stored as floats. Rendering problem not solved.
SOLVED: thank you for help. See my answer below.
On thing I did spot when glancing over your code is the following line from your vertex shader:
gl_Position = mProjection * mView * mModel * vec4(inPosition, 0);
That 0 should really be a 1.0.
In display() function
glDrawElements(GL_TRIANGLES, size / sizeof(GLubyte), GL_UNSIGNED_SHORT, 0);
should be changed to
glDrawElements(GL_TRIANGLES, size / sizeof(GLubyte), GL_UNSIGNED_BYTE, 0);
and in init()
glFrontFace(GL_CW);
to
glFrontFace(GL_CCW);
So the problem was that I passed to OpenGL incorrect data. Index array is of GLUbyte (1byte size each array element) but I for some reason decided it was GLushort (2bytes).
edit: doesn't matter a lot, but up vector (when generating camera matrix) should be not glm::vec3(0, 0, 1) but glm::vec3(0, 1, 0)