# OpenGL How are sprites implemented in DirectX?

This topic is 2914 days old which is more than the 365 day threshold we allow for new replies. Please post a new topic.

## Recommended Posts

Ok, this is probably the most noobish question I've asked on a forum, but for the life of me I just can't work it out or find anything to the depth I'm after on blogs / documentation site etc. The question is, how are sprites implemented in managed (ugh!!) direct x? And is is representative of other graphics APIs? The problem I'm having is that the Sprite class I'm using (Microsoft.DirectX.Direct3D.Sprite) doesn't have a width or height property, so am I to assume that the only way to resize a sprite is via scaling with a matrix? What I'm trying to achieve is using a sprite to display a texture on a 2D surface, but I want to set the size of the surface explicity (i.e. width=x etc) and have the texture resize to fit. I know this can be done using a mesh, but isn't that a bit overkill? My second question about Sprites (in this case exclusive to managed direct x) is why does Sprite.Draw have a position vector, when the class have a Transform matrix which I'm assuming should be used for the transforms, amongst which would be the position? Is it just for convenience? Finally (so sorry for the long post) should I not just be setting the world matrix to transform the coordinates of the sprite? I'm pretty sure this is what you do in normal direct x and open gl, or is the world matrix just for meshes and sprites are *special*? :s Agh! I just don't know why sprites a stumping me all of a sudded, I guess I just assumed from previous work (OpenGL maybe?) that they were re-sizable!! If any one could shed light on how they are implemented I'd really appreciate it! I'm starting to really loose it! lol Thanks, Andy.

##### Share on other sites
The D3DX sprite class is just a convenient utility so you don't have to construct your own dynamic vertex buffer. In raw D3DX9 it works somewhat like following:

-Begin method collects certain render states for sprite drawing, and saves the current states to its internal storage
-Draw method adds a quad to the sprite's internal vertex buffer (and possibly index buffer); this quad is transformed according to the parameters of the method as well as the matrix given in SetTransform.
-Flush method does the actual uploading and draw call to submit all geometry collected by the Draw method for rendering
-End method calls Flush and restores the render states set on the device prior to Begin.

##### Share on other sites
Hey, thanks a lot for the reply. That seems to makes sense!

So if its essentially a vertex buffer, why don't they offer methods or properties to size it? I.e. set the x/y coords of the vertexes? Would this not resize the texture to fit or is there more work involved?

Also, I've tried adding text using the same x,y coords as the meshes (as far as I'm aware the z coord of the meshes are at 0) and I've noticed that the meshes are drawn fine, but the text (on sprite) seems to be in a difference place. Is this because the sprites are only 2D and drawn in the projection space (i.e. just drawn to the screen coordinates)?

.. Really thought I understood all this! :s Any good links are also appricated! :)

##### Share on other sites
Quote:
 Original post by FunkiemonkeySo if its essentially a vertex buffer, why don't they offer methods or properties to size it? I.e. set the x/y coords of the vertexes? Would this not resize the texture to fit or is there more work involved?
That would stretch/shrink the texture, yes. It's not done that way simply because it's more often that you want your sprite to be shown with a 1:1 ratio of texels to pixels so it doesn't look distorted on screen. You can still do it by setting a scaling transform on the sprite (Although there's some weird caveats about that, have a search in these forums to see what I mean).

Quote:
 Original post by FunkiemonkeyAlso, I've tried adding text using the same x,y coords as the meshes (as far as I'm aware the z coord of the meshes are at 0) and I've noticed that the meshes are drawn fine, but the text (on sprite) seems to be in a difference place. Is this because the sprites are only 2D and drawn in the projection space (i.e. just drawn to the screen coordinates)?
Yup, exactly. Your mesh is in world space/coordinates, the sprite is drawn in screen space/coordinates.

##### Share on other sites
If you don't specifically set the sprite transform, it defaults to a scale of 1 along each axis with no translation. Your texture will be displayed without resizing.

If you want your texture to be displayed a specific size, you'll need to set a scaling transform with the scale being a ratio of the desired size to the original size.

Note: if you set a scaling transform for the sprite, it will also scale the translation (the position where the sprite is drawn) when the texture is rendered.

E.g., suppose you want to render a texture at twice its size, at a screen position of ( 200, 150 ).
D3DXMATRIX scale;float xscale = 2.0f, yscale = 2.0f; // want texture 2x size// generate scaling matrix for sizingD3DXMatrixScaling(&scale, xscale, yscale, 1 );sprite->SetTransform( &scale ); // set the scale for the textureD3DXVECTOR3 position( 200, 150, 0 ); // want position at 200, 150 onscreen// compensate for scaling to maintain position where desiredposition.x /= xscale;position.y /= yscale;sprite->Begin(...); // options as desiredsprite->Draw( texture, NULL, NULL, &position, desired_color );sprite->End();// to avoid confusion if you want to reuse the sprite for another texture, etc.D3DXMatrixIdentity(&scale);sprite->SetTransform(&scale);

##### Share on other sites
Excellent, that all makes sense now, thanks a lot for the explanations!

I really hate it when something you used to understand slips in your mind and gets lost somewhere....

Probably in the same place as the missing socks!

Thanks again anyway!

Andy.

• 12
• 10
• 11
• 18
• 13
• ### Similar Content

• Good Evening,
I want to make a 2D game which involves displaying some debug information. Especially for collision, enemy sights and so on ...
First of I was thinking about all those shapes which I need will need for debugging purposes: circles, rectangles, lines, polygons.
I am really stucked right now because of the fundamental question:
Where do I store my vertices positions for each line (object)? Currently I am not using a model matrix because I am using orthographic projection and set the final position within the VBO. That means that if I add a new line I would have to expand the "points" array and re-upload (recall glBufferData) it every time. The other method would be to use a model matrix and a fixed vbo for a line but it would be also messy to exactly create a line from (0,0) to (100,20) calculating the rotation and scale to make it fit.
If I proceed with option 1 "updating the array each frame" I was thinking of having 4 draw calls every frame for the lines vao, polygons vao and so on.
In addition to that I am planning to use some sort of ECS based architecture. So the other question would be:
Should I treat those debug objects as entities/components?
For me it would make sense to treat them as entities but that's creates a new issue with the previous array approach because it would have for example a transform and render component. A special render component for debug objects (no texture etc) ... For me the transform component is also just a matrix but how would I then define a line?
Treating them as components would'nt be a good idea in my eyes because then I would always need an entity. Well entity is just an id !? So maybe its a component?
Regards,
LifeArtist
• By QQemka
Hello. I am coding a small thingy in my spare time. All i want to achieve is to load a heightmap (as the lowest possible walking terrain), some static meshes (elements of the environment) and a dynamic character (meaning i can move, collide with heightmap/static meshes and hold a varying item in a hand ). Got a bunch of questions, or rather problems i can't find solution to myself. Nearly all are deal with graphics/gpu, not the coding part. My c++ is on high enough level.
Let's go:
Heightmap - i obviously want it to be textured, size is hardcoded to 256x256 squares. I can't have one huge texture stretched over entire terrain cause every pixel would be enormous. Thats why i decided to use 2 specified textures. First will be a tileset consisting of 16 square tiles (u v range from 0 to 0.25 for first tile and so on) and second a 256x256 buffer with 0-15 value representing index of the tile from tileset for every heigtmap square. Problem is, how do i blend the edges nicely and make some computationally cheap changes so its not obvious there are only 16 tiles? Is it possible to generate such terrain with some existing program?
Collisions - i want to use bounding sphere and aabb. But should i store them for a model or entity instance? Meaning i have 20 same trees spawned using the same tree model, but every entity got its own transformation (position, scale etc). Storing collision component per instance grats faster access + is precalculated and transformed (takes additional memory, but who cares?), so i stick with this, right? What should i do if object is dynamically rotated? The aabb is no longer aligned and calculating per vertex min/max everytime object rotates/scales is pretty expensive, right?
Drawing aabb - problem similar to above (storing aabb data per instance or model). This time in my opinion per model is enough since every instance also does not have own vertex buffer but uses the shared one (so 20 trees share reference to one tree model). So rendering aabb is about taking the model's aabb, transforming with instance matrix and voila. What about aabb vertex buffer (this is more of a cosmetic question, just curious, bumped onto it in time of writing this). Is it better to make it as 8 points and index buffer (12 lines), or only 2 vertices with min/max x/y/z and having the shaders dynamically generate 6 other vertices and draw the box? Or maybe there should be just ONE 1x1x1 cube box template moved/scaled per entity?
What if one model got a diffuse texture and a normal map, and other has only diffuse? Should i pass some bool flag to shader with that info, or just assume that my game supports only diffuse maps without fancy stuff?
There were several more but i forgot/solved them at time of writing
• By RenanRR
Hi All,
I'm reading the tutorials from learnOpengl site (nice site) and I'm having a question on the camera (https://learnopengl.com/Getting-started/Camera).
I always saw the camera being manipulated with the lookat, but in tutorial I saw the camera being changed through the MVP arrays, which do not seem to be camera, but rather the scene that changes:
#version 330 core layout (location = 0) in vec3 aPos; layout (location = 1) in vec2 aTexCoord; out vec2 TexCoord; uniform mat4 model; uniform mat4 view; uniform mat4 projection; void main() { gl_Position = projection * view * model * vec4(aPos, 1.0f); TexCoord = vec2(aTexCoord.x, aTexCoord.y); } then, the matrix manipulated:
..... glm::mat4 projection = glm::perspective(glm::radians(fov), (float)SCR_WIDTH / (float)SCR_HEIGHT, 0.1f, 100.0f); ourShader.setMat4("projection", projection); .... glm::mat4 view = glm::lookAt(cameraPos, cameraPos + cameraFront, cameraUp); ourShader.setMat4("view", view); .... model = glm::rotate(model, glm::radians(angle), glm::vec3(1.0f, 0.3f, 0.5f)); ourShader.setMat4("model", model);
So, some doubts:
- Why use it like that?
- Is it okay to manipulate the camera that way?
-in this way, are not the vertex's positions that changes instead of the camera?
- I need to pass MVP to all shaders of object in my scenes ?

What it seems, is that the camera stands still and the scenery that changes...
it's right?

Thank you

• Sampling a floating point texture where the alpha channel holds 4-bytes of packed data into the float. I don't know how to cast the raw memory to treat it as an integer so I can perform bit-shifting operations.

int rgbValue = int(textureSample.w);//4 bytes of data packed as color
// algorithm might not be correct and endianness might need switching.
vec3 extractedData = vec3(  rgbValue & 0xFF000000,  (rgbValue << 8) & 0xFF000000, (rgbValue << 16) & 0xFF000000);
extractedData /= 255.0f;

• While writing a simple renderer using OpenGL, I faced an issue with the glGetUniformLocation function. For some reason, the location is coming to be -1.
Anyone has any idea .. what should I do?