Opengl 4.3 gl_VertexID not incrementing with glDrawArrays - opengl

Question

I'm having difficulty in understanding why gl_VertexID is not properly incrementing for each new vertex in the code below for rendering "debug text". Hints/tips?
(Original code is referenced at the bottom of this post)
Hereafter is the vertex shader:
#version 430 core
layout( location = 0 ) in int Character;
out int vCharacter;
out int vPosition;
void main()
{
vPosition = gl_VertexID;
vCharacter = Character;
gl_Position = vec4(0, 0, 0, 1);
}
The geometry shader:
#version 430 core
layout(points) in;
layout(triangle_strip, max_vertices = 4) out;
in int vCharacter[1];
in int vPosition[1];
out vec2 gTexCoord;
uniform sampler2D Sampler;
uniform vec2 CellSize;
uniform vec2 CellOffset;
uniform vec2 RenderSize;
uniform vec2 RenderOrigin;
void main()
{
// Determine the final quad's position and size:
float x = RenderOrigin.x + float(vPosition[0]) * RenderSize.x * 2.0f;
float y = RenderOrigin.y;
vec4 P = vec4(x, y, 0, 1);
vec4 U = vec4(1, 0, 0, 0) * RenderSize.x;
vec4 V = vec4(0, 1, 0, 0) * RenderSize.y;
// Determine the texture coordinates:
int letter = vCharacter[0];
letter = clamp(letter - 32, 0, 96);
int row = letter / 16 + 1;
int col = letter % 16;
float S0 = CellOffset.x + CellSize.x * col;
float T0 = CellOffset.y + 1 - CellSize.y * row;
float S1 = S0 + CellSize.x - CellOffset.x;
float T1 = T0 + CellSize.y;
// Output the quad's vertices:
gTexCoord = vec2(S0, T1); gl_Position = P - U - V; EmitVertex();
gTexCoord = vec2(S1, T1); gl_Position = P + U - V; EmitVertex();
gTexCoord = vec2(S0, T0); gl_Position = P - U + V; EmitVertex();
gTexCoord = vec2(S1, T0); gl_Position = P + U + V; EmitVertex();
EndPrimitive();
}
The draw call and other relevant code:
glBindVertexArray(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
GLuint attribLocation = glGetAttribLocation(m_ProgramTextPrinter, "Character");
glVertexAttribIPointer(attribLocation, 1, GL_UNSIGNED_BYTE, 1, text.data()->c_str());
glEnableVertexAttribArray(attribLocation);
glDrawArrays(GL_POINTS, 0, text.data()->size());
Basically this code will be used for some text rendering. When I use this code, I see that my letters are put on top of each other. When I modify
glVertexAttribIPointer(attribLocation, 1, GL_UNSIGNED_BYTE, 1, text.data()->c_str());
into
glVertexAttribIPointer(attribLocation, 1, GL_UNSIGNED_BYTE, 2, text.data()->c_str());
I notice there is a shift in the x-direction as expected from the Geometry shader, nevertheless the letters are still on top of each other.
I'm using an NVIDIA Geforce GT 630M, driver version: 320.18 and an OpenGL 4.3 context.
Reference to the original author's code

Answer 1

I got the code working by using VBOs as Bartek hinted at: I basically replaced
glBindVertexArray(0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
GLuint attribLocation = glGetAttribLocation(m_ProgramTextPrinter, "Character");
glVertexAttribIPointer(attribLocation, 1, GL_UNSIGNED_BYTE, 1, text.data()->c_str());
glEnableVertexAttribArray(attribLocation);
glDrawArrays(GL_POINTS, 0, text.data()->size());
with
GLuint vaoID, bufferID;
glGenVertexArrays(1, &vaoID);
glBindVertexArray(vaoID);
glGenBuffers(1, &bufferID);
glBindBuffer(GL_ARRAY_BUFFER, bufferID);
glBufferData(GL_ARRAY_BUFFER, text.data()->size() * sizeof(GL_UNSIGNED_BYTE), text.data()->data(), GL_DYNAMIC_DRAW);
GLuint attribLocation = glGetAttribLocation(m_ProgramTextPrinter, "Character");
glVertexAttribIPointer(attribLocation, 1, GL_UNSIGNED_BYTE, 0, 0);
glEnableVertexAttribArray(attribLocation);
glDrawArrays(GL_POINTS, 0, text.data()->size());
glDeleteVertexArrays(1, &vaoID);
glDeleteBuffers(1, &bufferID);