OpenGL spritesheet shader - c++

Question

I'm staring to understand that a vertex Shader handles transformations of my texture. While the fragment Shader handles individual pixels. But this vector math is confusing.
What I'm trying to do is render a sprite from a sprite sheet. I can render a whole image just fine, but now i'm actually trying to write my own shader.
I think its more efficient to have the graphics card do the heavy lifting, that being said;
Currently I draw whole images like so:
In my init step,
void TextureRenderer::initRenderData()
{
// Configure VAO/VBO
game_uint VBO;
game_float vertices[] = {
// Pos // Tex
0.0f, 1.0f, 0.0f, 1.0f,
1.0f, 0.0f, 1.0f, 0.0f,
0.0f, 0.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f, 1.0f,
1.0f, 1.0f, 1.0f, 1.0f,
1.0f, 0.0f, 1.0f, 0.0f
};
glGenVertexArrays(1, &this->quadVAO);
glGenBuffers(1, &VBO);
glBindBuffer(GL_ARRAY_BUFFER, VBO);
glBufferData(GL_ARRAY_BUFFER, sizeof(vertices), vertices, GL_STATIC_DRAW);
glBindVertexArray(this->quadVAO);
glEnableVertexAttribArray(0);
glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 4 * sizeof(game_float), (GLvoid*)0);
glBindBuffer(GL_ARRAY_BUFFER, 0);
glBindVertexArray(0);
}
Then when its time to draw any texture:
void TextureRenderer::DrawTexture(Texture2D &texture, vec2 position, vec2 size, game_float rotate, vec3 color)
{
// Prepare transformations
this->shader->Use();
glm::mat4 model;
model = glm::translate(model, vec3(position, 0.0f)); // First translate (transformations are: scale happens first, then rotation and then finall translation happens; reversed order)
model = glm::translate(model, vec3(0.5f * size.x, 0.5f * size.y, 0.0f)); // Move origin of rotation to center of quad
model = glm::rotate(model, rotate, vec3(0.0f, 0.0f, 1.0f)); // Then rotate
model = glm::translate(model, vec3(-0.5f * size.x, -0.5f * size.y, 0.0f)); // Move origin back
model = glm::scale(model, vec3(size, 1.0f)); // Last scale
this->shader->SetMatrix4("model", model);
// Render textured quad
this->shader->SetVector3f("spriteColor", color);
glActiveTexture(GL_TEXTURE0);
texture.Bind();
glBindVertexArray(this->quadVAO);
glDrawArrays(GL_TRIANGLES, 0, 6);
glBindVertexArray(0);
}
TextureShader.vs:
#version 330 core
layout (location = 0) in vec4 vertex; // <vec2 position, vec2 texCoords>
out vec2 TexCoords;
uniform mat4 model;
uniform mat4 projection;
void main()
{
TexCoords = vertex.zw;
gl_Position = projection * model * vec4(vertex.xy, 0.0, 1.0);
}
Fragment Shader:
#version 330 core
in vec2 TexCoords; //Position
out vec4 color;
uniform sampler2D image;
uniform vec3 spriteColor;
void main()
{
color = vec4(spriteColor, 1.0) * texture(image, TexCoords);
}
Now that work all fine and dandy (assuming proper opengl setup ext.)
But id like to apply this to a Sprite sheet shader, and have the GPU handle the math to draw it.
void SpriteRenderer::drawSprite(Texture2D &texture, vec2 position,game_float spriteHeight,game_float spriteWidth,int frameIndex)
{
shader->Use();//Load a diffrent Shader here.
shader->SetInteger("frameindex", frameIndex);
shader->SetVector2f("position", position);
shader->SetFloat("spriteHeight", spriteHeight);
shader->SetFloat("spriteWidth", spriteWidth);
shader->SetMatrix4("model", model);
shader->SetVector3f("spriteColor", color);
glActiveTexture(GL_TEXTURE0); //Set texture to nothin
texture.Bind(); //Bind my texture.
glBindVertexArray(this->quadVAO); //Bind the fullscreen quad
glDrawArrays(GL_TRIANGLES, 0, 6); //Draw
glBindVertexArray(0); //Unbind the quad.
}
I assume:
Inside the vertex Shader, I manipulate the VAO quad to the position it is on the canvas then set the color of the pixles in the fragment shader to that spesific region.
How would that be done?
Or would it be better off for me to pre-calculate a VAO Array for each Sprite in a sprite class? Then each draw call would be:
void SpriteRenderer::drawSprite(Texture2D &texture, vec2 position,Sprite s)
Where the sprite has these vertices stored.
Iv seen:
Techniques for drawing spritesheets in OpenGL with shaders
Somewhat similar, but id like to have the GPU handle the math all together.