batch.cpp

class SpriteBatch {
    SpriteBatch(size) {
        self.size = size;
        self.idx = 0;
        self.buffer = glCreateBuffers();
        glBufferData(..., size);
    }

    void begin(Shader shader) {
        if (self.begun) error!("must end first!")
        if (self.shader != shader) {
            flush();
            self.shader = shader;
        }

        self.begun = true;
    }

    void draw(Sprite sprite) {
        if (self.texture != sprite.texture) {
            flush();
        }

        self.data[self.idx++] = sprite.vertex;
        self.data[self.idx++] = sprite.vertex;
        self.data[self.idx++] = sprite.vertex;
        
        self.data[self.idx++] = sprite.vertex;
        self.data[self.idx++] = sprite.vertex;
        self.data[self.idx++] = sprite.vertex;
    }

    void flush() {
        // setup vertex array and other material
        glUseProgram(self.shader);
        glBindBuffer(self.buffer);
        glBindTexture(self.texture);

        glBufferData(..., self.data);

        glDrawArrays(GL_TRIANGLES, 0, self.idx);

        reset();
    }

    void reset() {
        glBufferData(..., nullptr);
        self.idx = 0;
    }

    void end() {
        if (!self.begun) error!("must start first!")

        self.begun = false;

        self.flush();
    }
}