Draw two shapes on top of each other in geometry shader? - opengl

Question

With this small program I want to achieve:
Publish a point
Transform this point with vertex shader
Create a square and a triangle with geometry shader
Fill both the triangle and the square with fragment shader
Unfortunately, I cannot manage to superpose both shapes. I see either only the triangle or only the square. I tried to play with z but it doesn't change anything.
void main(void) {
finalColour = vec4(1.0, 0.5, 0.5, 1.0);
square(1.0, 0.0);
finalColour = vec4(0.0, 1.0, 1.0, 0.0);
triangle(vec3(0.0, 0.0, 0.0), angle[0], 1.0);
EndPrimitive();
}
void main(void) {
// finalColour = vec4(1.0, 0.5, 0.5, 1.0);
// square(1.0, 0.0);
finalColour = vec4(0.0, 1.0, 1.0, 0.0);
triangle(vec3(0.0, 0.0, 0.0), angle[0], 1.0);
EndPrimitive();
}
Main
#include <SFML/Graphics.hpp>
#include <GL/glew.h>
#include <vector>
#define WIDTH 800
int main() {
sf::RenderWindow window(sf::VideoMode(WIDTH, WIDTH), "Test");
sf::Shader shader;
shader.loadFromFile("shader.vert", "shader.geom", "shader.frag");
sf::Transform matrix = sf::Transform::Identity;
matrix.scale(1.0 / WIDTH, 1.0 / WIDTH);
sf::Glsl::Mat4 projectionViewMatrix = matrix;
shader.setUniform("projectionViewMatrix", projectionViewMatrix);
std::vector<GLfloat> vertices;
vertices.push_back(0.0); vertices.push_back(0.0); vertices.push_back(0.0);
while (window.isOpen()) {
sf::Event currEvent;
while (window.pollEvent(currEvent)) {
switch (currEvent.type) {
case(sf::Event::Closed):
window.close(); break;
}
}
window.clear(sf::Color::Black);
glEnable(GL_BLEND);
glBlendFunc(GL_ONE, GL_ONE_MINUS_SRC_ALPHA);
glVertexPointer(3, GL_FLOAT, 0, vertices.data());
glEnableClientState(GL_VERTEX_ARRAY);
glDrawArrays(GL_POINTS, 0, vertices.size() / 3);
glDisableClientState(GL_VERTEX_ARRAY);
sf::Shader::bind(&shader);
window.display();
}
}
Vertex
#version 150
in vec3 position;
out float angle;
uniform mat4 projectionViewMatrix;
void main(void){
gl_Position = projectionViewMatrix * vec4(position.xy, 0.0 ,1.0);
angle = position.z;
}
Geometry
#version 150
layout (points) in;
layout (triangle_strip, max_vertices = 6) out;
in float angle[];
out vec4 finalColour;
uniform mat4 projectionViewMatrix;
void createVertex(vec3 offset) {
vec4 actualOffset = vec4(offset, 1.0);
vec4 worldPosition = gl_in[0].gl_Position + actualOffset;
gl_Position = worldPosition;
EmitVertex();
}
void createAngularVertex(vec3 offset, float angle, float radius) {
vec4 actualOffset = vec4(offset, 1.0);
vec4 worldPosition = gl_in[0].gl_Position + actualOffset;
gl_Position = worldPosition;
gl_Position.x += cos(angle) * radius;
gl_Position.y += sin(angle) * radius;
EmitVertex();
}
void square(float size, float z) {
createVertex(vec3(-size, -size, z));
createVertex(vec3(size, -size, z));
createVertex(vec3(-size, size, z));
createVertex(vec3(size, size, z));
createVertex(vec3(size, -size, z));
createVertex(vec3(-size, size, z));
EndPrimitive();
}
void triangle(vec3 offset, float angle, float radius) {
float pi = 3.1415;
float angleOffset = 0.5;
createAngularVertex(offset, angle, radius);
createAngularVertex(offset, angle + pi + angleOffset, radius);
createAngularVertex(offset, angle + pi - angleOffset, radius);
EndPrimitive();
}
void main(void) {
finalColour = vec4(1.0, 0.5, 0.5, 1.0);
square(1.0, 0.0);
finalColour = vec4(0.0, 1.0, 1.0, 0.0);
triangle(vec3(0.0, 0.0, 0.0), angle[0], 0.1);
EndPrimitive();
}
Fragment
#version 150
in vec4 finalColour;
out vec4 out_Colour;
void main(void){
out_Colour = vec4(finalColour.rgb, 1.0);
}

Answer 1

The geometry shader creates 2 primitives, one with 6 vertices and one with 3 vertices, requiring a total of 9 vertices:
layout (triangle_strip, max_vertices = 6) out;
layout (triangle_strip, max_vertices = 9) out;