OpenGL texture shader not displaying to screen - opengl

Question

I'm trying to texture the ground with grass. Would someone mind looking through my steps to get a 2D texture to show up in 3D space? I haven't had any luck with online tutorials.
Here is my steps:
1) Call the sprite class initialization to set the vertex coordinates and uv data
void Sprite::init(vec3 bottomleft, vec3 topLeft, vec3 topRight, vec3 bottomRight, std::string texturePath)
{
_texture = ImageLoader::loadPNG(texturePath);
_points = { bottomleft.x, bottomleft.y, bottomleft.z, topLeft.x, topLeft.y, topLeft.z, topRight.x, topRight.y, topRight.z, topRight.x, topRight.y, topRight.z, bottomRight.x, bottomRight.y, bottomRight.z, bottomleft.x, bottomleft.y, bottomleft.z };
_uv = { 0.0f, 0.0f, 0.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 1.0f, 0.0f, 0.0f, 0.0f };
}
I use the uniform sampler and activate the texture
//draw ground texture
glUniform1i(samplerLocation, 0);
glActiveTexture(GL_TEXTURE0);
_grassTexture.draw();
The draw function is implemented as follows, which puts the data in the buffer and draws the triangle:
void Sprite::draw()
{
if (_vboID == 0)
{
glGenBuffers(1, &_vboID);
}
glBindTexture(GL_TEXTURE_2D, _texture.id);
glBindBuffer(GL_ARRAY_BUFFER, _vboID);
glBufferData(GL_ARRAY_BUFFER, _points.size() * sizeof(float) + _uv.size() * sizeof(float), nullptr, GL_STATIC_DRAW);
glBufferSubData(GL_ARRAY_BUFFER, 0, _points.size() * sizeof(float), &_points.front());
glBufferSubData(GL_ARRAY_BUFFER, _points.size() * sizeof(float), _uv.size() * sizeof(float), &_uv.front());
glEnableVertexAttribArray(0);
glEnableVertexAttribArray(1);
//position attribute pointer
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, &_points.front());
//uv attribute pointer
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, &_uv.front());
glDrawArrays(GL_TRIANGLES, 0, 6);
glDisableVertexAttribArray(0);
glDisableVertexAttribArray(1);
glBindBuffer(GL_ARRAY_BUFFER, 0);
}
The vertex shader:
#version 400
in vec4 vertexPosition;
in vec2 vertexUV;
out vec4 fragmentColor;
out vec2 fragmentUV;
uniform mat4 MVP;
uniform vec4 COLOR;
void main()
{
gl_Position = MVP * vertexPosition;
fragmentColor = COLOR;
fragmentUV = vec2(vertexUV.x, 1.0 - vertexUV.y);
}
and fragment shader:
#version 400
in vec4 fragmentColor;
in vec2 fragmentUV;
out vec4 fragColor;
uniform sampler2D SAMPLER;
void main()
{
vec4 textureColor = texture(SAMPLER, fragmentUV);
fragColor = textureColor * fragmentColor;
}
At this point, nothing displays in the screen. I do know that the textureColor in the fragment shader is green, so it appears the uniform is being set correctly. My best guess is that I'm either missing a texture initialization step or am not filling the buffer correctly.

Answer 1

I think there's a problem with the pointer parameter in your calls to glVertexAttribPointer. You're passing the address of your _points and _uv arrays, but you should be passing the offset relative to the base of your vbo.
Try:
//position attribute pointer
glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 0, nullptr);
//uv attribute pointer
glVertexAttribPointer(1, 2, GL_FLOAT, GL_FALSE, 0, (const GLvoid*)(_points.size() * sizeof(float)));