# Introduction to lights 2d

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In-Practice/2D-Game/Rendering-Sprites

To bring some life to the currently blachồng abyss of our game world, we will render sprites to fill the void. A sprite has many definitions, but it"s effectively not much more than a 2 chiều image used together with some data to position it in a larger world (e.g. position, rotation, và size). Basically, sprites are the render-able image/texture objects we use in a 2D game.

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We can, just lượt thích we did in previous chapters, create a 2D shape out of vertex data, pass all data lớn the GPU, and transform it all by h&. However, in a larger application like this we rather have some abstractions on rendering 2D shapes. If we were to manually define these shapes và transformations for each object, it"ll quickly get messy.

In this chapter we"ll define a rendering class that allows us khổng lồ render a large amount of quality sprites with a minimal amount of code. This way, we"re abstracting the gameplay code from the gritty OpenGL rendering code as is commonly done in larger projects. First, we have to lớn phối up a proper projection matrix though.

## 2 chiều projection matrix

We know from the coordinate systems chapter that a projection matrix converts all view-space coordinates to lớn clip-space (& then khổng lồ normalized device) coordinates. By generating the appropriate projection matrix we can work with different coordinates that are easier lớn work with, compared to directly specifying all coordinates as normalized device coordinates.

We don"t need any perspective sầu applied khổng lồ the coordinates, since the game is entirely in 2D, so an orthographic projection matrix would suit the rendering quite well. Because an orthographic projection matrix directly transforms all coordinates lớn normalized device coordinates, we can choose to lớn specify the world coordinates as screen coordinates by defining the projection matrix as follows:

glm::mat4 projection = glm::ortho(0.0f, 800.0f, 600.0f, 0.0f, -1.0f, 1.0f); The first four arguments specify in order the left, right, bottom, and top part of the projection frustum. This projection matrix transforms all x coordinates between 0 and 800 to -1 and 1, & all y coordinates between 0 and 600 to -1 & 1. Here we specified that the top of the frustum has a y coordinate of 0, while the bottom has a y coordinate of 600. The result is that the top-left coordinate of the scene will be at (0,0) và the bottom-right part of the screen is at coordinate (800,600), just lượt thích screen coordinates; the world-space coordinates directly correspond to the resulting pixel coordinates. This allows us lớn specify all vertex coordinates equal to lớn the px coordinates they end up in on the screen, which is rather intuitive sầu for 2D games.

## Rendering sprites

Rendering an actual sprite shouldn"t be too complicated. We create a textured quad that we can transform with a mã sản phẩm matrix, after which we project it using the previously defined orthographic projection matrix.

Since Breakout is a single-scene game, there is no need for a view/camera matrix. Using the projection matrix we can directly transsize the world-space coordinates to normalized device coordinates.

To transsize a sprite, we use the following vertex shader:

#version 330 corelayout (location = 0) in vec4 vertex; // out vec2 TexCoords;unisize mat4 model;unisize mat4 projection;void main() TexCoords = vertex.zw; gl_Position = projection * Mã Sản Phẩm * vec4(vertex.xy, 0.0, 1.0); Note that we store both the position and texture-coordinate data in a single vec4 variable. Because both the position and texture coordinates contain two floats, we can combine them in a single vertex attribute.

The fragment shader is relatively straightforward as well. We take a texture & a color vector that both affect the final color of the fragment. By having a unikhung color vector, we can easily change the color of sprites from the game-code:

#version 330 corein vec2 TexCoords;out vec4 color;unisize sampler2 chiều image;unisize vec3 spriteColor;void main() color = vec4(spriteColor, 1.0) * texture(image, TexCoords); To make the rendering of sprites more organized, we define a SpriteRenderer class that is able to lớn render a sprite with just a single function. Its definition is as follows:

class SpriteRenderer public: SpriteRenderer(Shader &shader); ~SpriteRenderer(); void DrawSprite(Texture2 chiều &texture, glm::vec2 position, glm::vec2 size = glm::vec2(10.0f, 10.0f), float rotate = 0.0f, glm::vec3 color = glm::vec3(1.0f)); private: Shader shader; unsigned int quadVAO; void initRenderData();; The SpriteRenderer class hosts a shader object, a single vertex array object, & a render and initialization function. Its constructor takes a shader object that it uses for all future rendering.

### Initialization

First, let"s delve sầu inkhổng lồ the initRenderData function that configures the quadVAO:

void SpriteRenderer::initRenderData() // configure VAO/VBO unsigned int VBO; 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(float), (void*)0); glBindBuffer(GL_ARRAY_BUFFER, 0); glBindVertexArray(0); Here we first define a set of vertices with (0,0) being the top-left corner of the quad. This means that when we apply translation or scaling transformations on the quad, they"re transformed from the top-left position of the quad. This is commonly accepted in 2 chiều graphics and/or GUI systems where elements" positions correspond lớn the top-left corner of the elements.

Next we simply sent the vertices to lớn the GPU and configure the vertex attributes, which in this case is a single vertex attribute. We only have sầu khổng lồ define a single VAO for the sprite renderer since all sprites chia sẻ the same vertex data.

### Rendering

Rendering sprites is not too difficult; we use the sprite renderer"s shader, configure a Mã Sản Phẩm matrix, and mix the relevant uniforms. What is important here is the order of transformations:

void SpriteRenderer::DrawSprite(Texture2 chiều &texture, glm::vec2 position, glm::vec2 kích thước, float rotate, glm::vec3 color) // prepare transformations this->shader.Use(); glm::mat4 model = glm::mat4(1.0f); Mã Sản Phẩm = glm::translate(Mã Sản Phẩm, glm::vec3(position, 0.0f)); model = glm::translate(mã sản phẩm, glm::vec3(0.5f * kích thước.x, 0.5f * size.y, 0.0f)); Model = glm::rotate(model, glm::radians(rotate), glm::vec3(0.0f, 0.0f, 1.0f)); Model = glm::translate(model, glm::vec3(-0.5f * size.x, -0.5f * size.y, 0.0f)); Model = glm::scale(model, glm::vec3(kích thước, 1.0f)); this->shader.SetMatrix4("model", model); this->shader.SetVector3f("spriteColor", color); glActiveTexture(GL_TEXTURE0); texture.Bind(); glBindVertexArray(this->quadVAO); glDrawArrays(GL_TRIANGLES, 0, 6); glBindVertexArray(0); When trying to position objects somewhere in a scene with rotation và scaling transformations, it is advised to first scale, then rotate, và finally translate the object. Because multiplying matrices occurs from right lớn left, we transsize the matrix in reverse order: translate, rotate, và then scale.

The rotation transformation may still seem a bit daunting. We know from the transformations chapter that rotations always revolve sầu around the origin (0,0). Because we specified the quad"s vertices with (0,0) as the top-left coordinate, all rotations will rotate around this point of (0,0). The origin of rotation is at the top-left of the quad, which produces undesirable results. What we want khổng lồ bởi is move the origin of rotation to lớn the center of the quad so the quad neatly rotates around this origin, instead of rotating around the top-left of the quad. We solve this by translating the quad by half its kích thước first, so its center is at coordinate (0,0) before rotating. Since we first scale the quad, we have khổng lồ take the size of the sprite into lớn trương mục when translating lớn the sprite"s center, which is why we multiply with the sprite"s kích thước vector. Once the rotation transformation is applied, we reverse the previous translation.

Combining all these transformations, we can position, scale, & rotate each sprite in any way we like. Below you can find the complete source code of the sprite renderer:

## Hello sprite

With the SpriteRenderer class we finally have the ability to lớn render actual images lớn the screen! Let"s initialize one within the game code và load our favorite texture while we"re at it: 