【OpenGL】OpenGL游戏案例(二)

特殊效果

为提高游戏的趣味性，在游戏中提供了六种特殊效果。

数据结构

PowerUp

类只存储存活数据，实际逻辑在游戏代码中通过Type字段来区分执行

class PowerUp : public GameObject
{
public:// powerup statestd::string Type;float       Duration;bool        Activated;// constructorPowerUp(std::string type, glm::vec3 color, float duration, glm::vec2 position, Texture2D texture): GameObject(position, POWERUP_SIZE, texture, color, VELOCITY), Type(type), Duration(duration), Activated() { }
};

Game中存在容器存储目前存活的PowerUp对象

std::vector<PowerUp>  PowerUps;

生成逻辑

当玩家消灭一个方块后，按固定概率随机生成或不生成一个随机能力的砖块。

//Game::DoCollision()// destroy block if not solid
if (!box.IsSolid)
{box.Destroyed = true;this->SpawnPowerUps(box);
}

生成策略

bool ShouldSpawn(unsigned int chance)
{unsigned int random = rand() % chance;return random == 0;
}
void Game::SpawnPowerUps(GameObject& block)
{if (ShouldSpawn(75)) // 1 in 75 chancethis->PowerUps.push_back(PowerUp("speed", glm::vec3(0.5f, 0.5f, 1.0f), 0.0f, block.Position, ResourceManager::GetTexture("powerup_speed")));if (ShouldSpawn(75))this->PowerUps.push_back(PowerUp("sticky", glm::vec3(1.0f, 0.5f, 1.0f), 20.0f, block.Position, ResourceManager::GetTexture("powerup_sticky")));if (ShouldSpawn(75))this->PowerUps.push_back(PowerUp("pass-through", glm::vec3(0.5f, 1.0f, 0.5f), 10.0f, block.Position, ResourceManager::GetTexture("powerup_passthrough")));if (ShouldSpawn(75))this->PowerUps.push_back(PowerUp("pad-size-increase", glm::vec3(1.0f, 0.6f, 0.4), 0.0f, block.Position, ResourceManager::GetTexture("powerup_increase")));if (ShouldSpawn(15)) // Negative powerups should spawn more oftenthis->PowerUps.push_back(PowerUp("confuse", glm::vec3(1.0f, 0.3f, 0.3f), 15.0f, block.Position, ResourceManager::GetTexture("powerup_confuse")));if (ShouldSpawn(15))this->PowerUps.push_back(PowerUp("chaos", glm::vec3(0.9f, 0.25f, 0.25f), 15.0f, block.Position, ResourceManager::GetTexture("powerup_chaos")));
}

更新逻辑

生成完后会在Update中调用以下函数下落更新，并每帧检查是否与玩家发生碰撞

不同状态下能力内部标志位变化：

	Destoryed	Activated
下落状态	false	false
与玩家碰撞后	true	true
倒计时结束后	true	false

Destroyed决定是否要渲染其图像，Activated决定是否要启用其计时器，最后的状态则决定了是否要将其移除出列表

刚碰撞时根据Type字段执行附加能力的逻辑，倒计时结束后执行取消附加能力的逻辑。流程完毕后移除出数组

//绘制
for (PowerUp& powerUp : this->PowerUps)if (!powerUp.Destroyed)powerUp.Draw(*Renderer);//检查碰撞
for (PowerUp& powerUp : this->PowerUps)
{if (!powerUp.Destroyed){if (powerUp.Position.y >= this->Height)powerUp.Destroyed = true;if (CheckCollision(*Player, powerUp)){	// collided with player, now activate powerupActivatePowerUp(powerUp);powerUp.Destroyed = true;powerUp.Activated = true;}}
}//启用能力
void ActivatePowerUp(PowerUp& powerUp)
{if (powerUp.Type == "speed"){Ball->Velocity *= 1.2;}else if (powerUp.Type == "sticky"){Ball->Sticky = true;Player->Color = glm::vec3(1.0f, 0.5f, 1.0f);}else if (powerUp.Type == "pass-through"){Ball->PassThrough = true;Ball->Color = glm::vec3(1.0f, 0.5f, 0.5f);}else if (powerUp.Type == "pad-size-increase"){Player->Size.x += 50;}else if (powerUp.Type == "confuse"){if (!Effects->Chaos)Effects->Confuse = true; // only activate if chaos wasn't already active}else if (powerUp.Type == "chaos"){if (!Effects->Confuse)Effects->Chaos = true;}
}//每帧更新，轮询何时撤销能力
void Game::UpdatePowerUps(float dt)
{for (PowerUp& powerUp : this->PowerUps){powerUp.Position += powerUp.Velocity * dt;if (powerUp.Activated){powerUp.Duration -= dt;if (powerUp.Duration <= 0.0f){// remove powerup from list (will later be removed)powerUp.Activated = false;// deactivate effectsif (powerUp.Type == "sticky"){if (!IsOtherPowerUpActive(this->PowerUps, "sticky")){	// only reset if no other PowerUp of type sticky is activeBall->Sticky = false;Player->Color = glm::vec3(1.0f);}}else if (powerUp.Type == "pass-through"){if (!IsOtherPowerUpActive(this->PowerUps, "pass-through")){	// only reset if no other PowerUp of type pass-through is activeBall->PassThrough = false;Ball->Color = glm::vec3(1.0f);}}else if (powerUp.Type == "confuse"){if (!IsOtherPowerUpActive(this->PowerUps, "confuse")){	// only reset if no other PowerUp of type confuse is activeEffects->Confuse = false;}}else if (powerUp.Type == "chaos"){if (!IsOtherPowerUpActive(this->PowerUps, "chaos")){	// only reset if no other PowerUp of type chaos is activeEffects->Chaos = false;}}}}}// Remove all PowerUps from vector that are destroyed AND !activated (thus either off the map or finished)// Note we use a lambda expression to remove each PowerUp which is destroyed and not activatedthis->PowerUps.erase(std::remove_if(this->PowerUps.begin(), this->PowerUps.end(),[](const PowerUp& powerUp) { return powerUp.Destroyed && !powerUp.Activated; }), this->PowerUps.end());
}

文本渲染

文本渲染部分依赖于一个库FreeType，在项目中只拿来读取ttf生成像素数据，然后记录在自定义的Character结构中。

// 宽度、高度、左上角偏移、水平距离
struct Character
{unsigned int TextureID;glm::ivec2    Size;glm::ivec2    Bearing;unsigned int  Advance;
};

创建文字渲染器类TextRenderer来负责文字的渲染

类结构

class TextRenderer
{
public:// 预处理记录的需要的字符内容（借助FreeType）std::map<char, Character> Characters;// 文字渲染Shader，就是渲染一个四边形，然后采样纹理并渲染上去Shader TextShader;TextRenderer(unsigned int width, unsigned int height);void Load(std::string font, unsigned int fontSize);void RenderText(std::string text, float x, float y, float scale, glm::vec3 color = glm::vec3(1.0f));private:unsigned int VAO, VBO;
};

构造函数

构造函数中负责初始化shader参数，初始化VAO和VBO，但VBO的具体顶点数据会在绘制时动态计算出来

TextRenderer::TextRenderer(unsigned int width, unsigned int height)
{// load and configure shaderthis->TextShader = ResourceManager::LoadShader("res/shaders/text.vs", "res/shaders/text.frag", nullptr, "text");this->TextShader.SetMatrix4("projection", glm::ortho(0.0f, static_cast<float>(width), static_cast<float>(height), 0.0f), true);this->TextShader.SetInteger("text", 0);// configure VAO/VBO for texture quadsglGenVertexArrays(1, &this->VAO);glGenBuffers(1, &this->VBO);//绑定VAO，VBOglBindVertexArray(this->VAO);glBindBuffer(GL_ARRAY_BUFFER, this->VBO);//填充VBO数据glBufferData(GL_ARRAY_BUFFER, sizeof(float) * 6 * 4, NULL, GL_DYNAMIC_DRAW);//规划VBO数据布局glEnableVertexAttribArray(0);glVertexAttribPointer(0, 4, GL_FLOAT, GL_FALSE, 4 * sizeof(float), 0);//解绑glBindBuffer(GL_ARRAY_BUFFER, 0);glBindVertexArray(0);
}

加载函数

外部提供字体文件（.ttf）路径和字体大小，内部利用FreeType将前128字符转换为使用Characters存储

void TextRenderer::Load(std::string font, unsigned int fontSize)
{// 如果之前已经Load过，清除this->Characters.clear();// 初始化并加载 FreeType libraryFT_Library ft;if (FT_Init_FreeType(&ft))std::cout << "ERROR::FREETYPE: Could not init FreeType Library" << std::endl;// 将字符加载为faceFT_Face face;if (FT_New_Face(ft, font.c_str(), 0, &face))std::cout << "ERROR::FREETYPE: Failed to load font" << std::endl;// 设置加载字体的大小，这里是设置为 fontSize 参数指定的大小。第一个参数为 0，表示不限制宽度，第二个参数是目标字体大小FT_Set_Pixel_Sizes(face, 0, fontSize);// 关闭了 OpenGL 中的字节对齐限制，使得字节数据可以按 1 字节对齐，这样可以避免在纹理生成时出现内存填充问题glPixelStorei(GL_UNPACK_ALIGNMENT, 1);// 通过循环加载前 128 个 ASCII 字符。for (GLubyte c = 0; c < 128; c++){// FT_Load_Char 用来加载字符的字形信息，如果加载失败，则输出错误信息并跳过该字符if (FT_Load_Char(face, c, FT_LOAD_RENDER)){std::cout << "ERROR::FREETYTPE: Failed to load Glyph" << std::endl;continue;}// 为每个字符生成一个纹理unsigned int texture;glGenTextures(1, &texture);glBindTexture(GL_TEXTURE_2D, texture);//使用 GL_RED 格式来存储单通道的灰度数据glTexImage2D(GL_TEXTURE_2D,0,GL_RED,face->glyph->bitmap.width,face->glyph->bitmap.rows,0,GL_RED,GL_UNSIGNED_BYTE,face->glyph->bitmap.buffer);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);//将原始数据转换为Character数组Character character = {texture,glm::ivec2(face->glyph->bitmap.width, face->glyph->bitmap.rows),glm::ivec2(face->glyph->bitmap_left, face->glyph->bitmap_top),face->glyph->advance.x};Characters.insert(std::pair<char, Character>(c, character));}// 清理资源glBindTexture(GL_TEXTURE_2D, 0);FT_Done_Face(face);FT_Done_FreeType(ft);
}

渲染函数

• 使用并设置文字shader，使用当前的VAO
• 遍历所有提供的字符，在Characters中取出对应的数据
• 计算位置长宽，更新顶点缓存，绑定记录的纹理
• 绘制完后偏移光标位置

void TextRenderer::RenderText(std::string text, float x, float y, float scale, glm::vec3 color)
{// activate corresponding render state	this->TextShader.Use();this->TextShader.SetVector3f("textColor", color);glActiveTexture(GL_TEXTURE0);glBindVertexArray(this->VAO);// iterate through all charactersstd::string::const_iterator c;for (c = text.begin(); c != text.end(); c++){Character ch = Characters[*c];// 计算位置和长宽float xpos = x + ch.Bearing.x * scale;float ypos = y + (this->Characters['H'].Bearing.y - ch.Bearing.y) * scale;float w = ch.Size.x * scale;float h = ch.Size.y * scale;// 为每个字符更新对应的VBO缓存float vertices[6][4] = {{ xpos,     ypos + h,   0.0f, 1.0f },{ xpos + w, ypos,       1.0f, 0.0f },{ xpos,     ypos,       0.0f, 0.0f },{ xpos,     ypos + h,   0.0f, 1.0f },{ xpos + w, ypos + h,   1.0f, 1.0f },{ xpos + w, ypos,       1.0f, 0.0f }};// 绑定指定的纹理glBindTexture(GL_TEXTURE_2D, ch.TextureID);// update content of VBO memoryglBindBuffer(GL_ARRAY_BUFFER, this->VBO);glBufferSubData(GL_ARRAY_BUFFER, 0, sizeof(vertices), vertices);glBindBuffer(GL_ARRAY_BUFFER, 0);// render quadglDrawArrays(GL_TRIANGLES, 0, 6);// 更新光标位置x += (ch.Advance >> 6) * scale; // bitshift by 6 to get value in pixels (1/64th times 2^6 = 64)}glBindVertexArray(0);glBindTexture(GL_TEXTURE_2D, 0);
}