we can clip the frame using frameWithTexture of CCSpriteFrame through CCSpriteSheet.but what is the difference between clipping node and this CCSpriteFrame?
Clipping is not the same as sprite frames.
A sprite frame defines an area on a texture, which in turn allows a sprite to draw that part of a texture. It enables the use of a texture atlas, ie multiple images combined into a single texture. This is a Cocos2D feature.
A clipping node defines an area on the screen on which content is drawn, but everything that is outside that frame isn't drawn (clipped). The clipping happens exactly at the clipping boundary, ie. only the part of a sprite that is within the clipping region is drawn. This is an OpenGL feature, typically wrapped in a Cocos2D node for easier placement.
Clipping is a simplified form of a stencil in that it can only define a rectangular area.
Related
In a 3D scene in Godot, I am attempting to create a pixel-perfect outline for a Spatial shader (applied after a pixelation effect to ensure the same resolution). To achieve this, I would like to modify pixels directly adjacent to the target mesh.
That said, I have a hunch that I simply cannot modify pixels outside of a mesh's area in screespace, and that I would have to use a separate donor mesh to achieve this effect. The issue with this is that I'm even more unsure of how to access an external mesh (I am fine applying the same pixel perfect effect to all meshes on-screen, but it would have to be pixel-perfect).
A secondary solution that I may have to settle with: do an inwards bleed for the outline, sacrificing the outermost pixels for the outline, which would be acceptable compromise.
You can render just the elements you want to a Viewport using cull_mask as I just described in another answer here.
Now, you can take the texture from that Viewport use a ViewportTexture (make sure it is local to the scene and you are using it a Node placed after the Viewport in the scene tree) and process it using a shader.
I suggest you make the background of the Viewport transparent, so you can use the alpha channel to check if a pixel is rendered or not. The outline pixels will be those which are not rendered but are adjacent to a pixel that was rendered.
This is the idea behind convolution edge detection. See Kernel (image processing).
I have a small custom ray tracer that I am integrating in an application. There is a resizable OpenGL window that represents the camera into the scene. I have a perspective matrix that adjusts the overall aspect ratio when the window resizes (basic setup).
Now I would like to draw a transparent rectangle over the window representing the width x height of the render so a user knows exactly what will be rendered. How could this be done? How can I place the rectangle accurately? The user can enter different output resolutions for the ray tracer.
If I understand well your problem, I think that your overlay represents the new "screen" in your perspective frustum.
Redefine then a perspective matrix for the render, in which the overlay 4 corners define the "near" projection plane.
I am using opengl and c++ doing image processing. The idea is simple, I will load an image, draw a polygon by clicking and then apply an effect (desaturation for instance) only to the pixels in the interior of the polygon shape just created.
Can anyone give me any direction on how to limit the effect to the pixels within the interior of the polygon? Loading the image and drawing the polygon is not a problem
Supposing the following situation :
The picture on which you want to apply the effect takes the whole screen
The picture is rendered using opengl , probably through a simple shader, with the picture passed as a texture
You can do the following approach :
consider the screen as being a big texture
you draw a polygon, which will be rendered on top of the rendered texture
inside the polygon's vertices insert the uv's coresponding to the 2D coordinates on the screen (so from screen space to uv space (0 , 1 ) )
draw the picture normaly
on top of the picture draw your polygon using the same picture as texture, but with a different shader
So instead of trying to desaturate a specific region from your picture, create a polygon on top of that region with the same picture, and desaturate that new polygon.
This would help you in avoiding the stencil buffer.
Another approach would be to create the polygon, but draw it only on the stencil buffer, before the picture is drawn.
I have a question about clipping in OpenGL. So I have a small viewport and I want to render one part of a large image. If I draw a large image like
glEnable(GL_TEXTURE_RECTANGLE)
glColor3f(1,1,1)
glTexCoord2f(0,height)
glVertex2f(0,0)
glTexdoord2f(width,height)
glVertex2f(width,0)
glTexCoord2f(width,0)
glVertex2f(width,height)
glTexCoord(0,0)
glVertex2f(0,height)
The width and height is the size of the image(texture), which is much larger than the viewport.
My question is: Is OpenGL going to firstly clip the rectangle with respect to the size of viewport and then draw, or firstly render the whole image and then clip?
It will first clip the geometry, then draw. More specifically, OpenGL does all the geometry processing before going down to render individual framebuffer elements (pixels). Here's a relevant quote from the 3.3 GL spec (Section 2.4):
The final resulting primitives are clipped to a viewing volume in
preparation for the next stage, rasterization. The rasterizer produces
a series of framebuffer addresses and values using a two-dimensional
description of a point, line segment, or polygon.
I'm doing a 3D asteroids game in windows (using OpenGL and GLUT) where you move in space through a bunch of obstacles and survive. I'm looking for a way to set an image background against the boring bg color options. I'm new to OpenGL and all i can think of is to texture map a sphere and set it to a ridiculously large radius. What is the standard way of setting image bg in a 3d game?
The standard method is to draw two texture mapped triangles, whose coordinates are x,y = +-1, z=0, w=1 and where both camera and perspective matrices are set to identity matrix.
Of course in the context of a 'space' game, where one could want the background to rotate, the natural choice is to render a cube with cubemap (perhaps showing galaxies). As the depth buffering is turned off during the background rendering, the cube doesn't even have to be "infinitely" large. A unit cube will do, as there is no way to find out how close the camera is to the object.