OpenGL: Multisampling texture y axis inverted? - opengl

Question

I have a problem with a multisampled texture. It seems after blitting it to another surface for rendering, it's flipped upside down. What might cause that ? Should I provide some code ?
edit: Well, it's gonna be a lot of code, but here we go. This is how I create my surfaces / textures:
protected override void Create(int width, int height, SurfaceFormat format)
{
this.format = format;
bool multisample = format.Multisampling > 0;
int samples = Math.Max(0, Math.Min(format.Multisampling, 4));
format.TextureTarget = multisample ? TextureTarget.Texture2DMultisample : format.TextureTarget;
format.MipMapping = format.MipMapping && format.TextureTarget == TextureTarget.Texture2D;
Width = width;
Height = height;
textureHandle = GL.GenTexture();
//bind texture
GL.BindTexture(format.TextureTarget, textureHandle);
Log.Error("Bound Texture: " + GL.GetError());
if (format.TextureTarget == TextureTarget.Texture2D)
{
GL.TexParameter(format.TextureTarget, TextureParameterName.TextureMinFilter, (int)(format.MipMapping ? TextureMinFilter.LinearMipmapLinear : TextureMinFilter.Linear));
GL.TexParameter(format.TextureTarget, TextureParameterName.TextureMagFilter, (int)TextureMagFilter.Linear);
GL.TexParameter(format.TextureTarget, TextureParameterName.TextureWrapS, (int)format.WrapMode);
GL.TexParameter(format.TextureTarget, TextureParameterName.TextureWrapT, (int)format.WrapMode);
}
Log.Debug("Created Texture Parameters: " + GL.GetError());
if (samples < 1)
GL.TexImage2D(format.TextureTarget, 0, format.InternalFormat, Width, Height, 0, format.PixelFormat, format.SourceType, format.Pixels);
else
GL.TexImage2DMultisample(TextureTargetMultisample.Texture2DMultisample, samples, format.InternalFormat, Width, Height, true);
if (format.MipMapping)
GL.GenerateMipmap(GenerateMipmapTarget.Texture2D);
Log.Debug("Created Image: " + GL.GetError());
//unbind texture
GL.BindTexture(format.TextureTarget, 0);
//create depthbuffer
if (format.DepthBuffer)
{
GL.GenRenderbuffers(1, out dbHandle);
GL.BindRenderbuffer(RenderbufferTarget.RenderbufferExt, dbHandle);
if(multisample)
GL.RenderbufferStorageMultisample(RenderbufferTarget.RenderbufferExt, samples, RenderbufferStorage.DepthComponent24, Width, Height);
else
GL.RenderbufferStorage(RenderbufferTarget.RenderbufferExt, RenderbufferStorage.DepthComponent24, Width, Height);
}
//create fbo
fboHandle = GL.GenFramebuffer();
GL.BindFramebuffer(FramebufferTarget.FramebufferExt, fboHandle);
GL.FramebufferTexture2D(FramebufferTarget.FramebufferExt, FramebufferAttachment.ColorAttachment0Ext, format.TextureTarget, textureHandle, 0);
if (format.DepthBuffer)
GL.FramebufferRenderbuffer(FramebufferTarget.FramebufferExt, FramebufferAttachment.DepthAttachmentExt, RenderbufferTarget.RenderbufferExt, dbHandle);
Log.Debug("Framebuffer status: " + GL.CheckFramebufferStatus(FramebufferTarget.FramebufferExt));
Log.Debug("Created Framebuffer: " + GL.GetError());
GL.BindFramebuffer(FramebufferTarget.FramebufferExt, 0);
}
creation:
var sf = SurfaceFormat.Surface2D;
sf.Multisampling = 4;
multisampler = new Surface(Window.Width, Window.Height, sf);
Now in the render loop I do the following:
//Render entire scene to multisampler
SceneRenderer.RenderMultisampled(ActiveCamera, multisampler, time);
//blit sampler to my material input texture
multisampler.CloneTo(postEffect.Textures["_tex"]);
//blit this texture to my "Canvas" (basically a surface with additional drawing methods. The canvas material is use as a texture for a quad in my scene, thus rendering a copy of the output image to a plane.
postEffect.Textures["_tex"].CloneTo(canvas.Surface);
//This would be the same but via rendering with a quad instead of blitting. Has the same result
//canvas.Clear();
//canvas.DrawMaterial(postEffect);
//clear framebuffer
GL.BindFramebuffer(FramebufferTarget.Framebuffer, 0);
//Set viewport
GL.Viewport(0, 0, Window.Width, Window.Height);
//use material (bind shader & shader params) and draw the scene.
postEffect.Use();
Helper.DrawScreenQuad();
GL.UseProgram(0);
If this is not enough, I can also post the shaders & mesh code.
EDIT2: Okay everything is now working as expected EXCEPT when I use canvas.draw() instead of blitting the texture. The draw method looks like this:
public void DrawMaterial(Material material)
{
GL.Viewport(0, 0, Surface.Width, Surface.Height);
Surface.BindFramebuffer();
material.Use();
Helper.DrawScreenQuad();
GL.UseProgram(0);
GL.BindFramebuffer(FramebufferTarget.Framebuffer, 0);
}
Draw screen quad:
public static void DrawScreenQuad()
{
GL.Begin(PrimitiveType.Quads);
GL.TexCoord2(0, 1);
GL.Vertex2(-1, -1);
GL.TexCoord2(1, 1);
GL.Vertex2(1, -1);
GL.TexCoord2(1, 0);
GL.Vertex2(1, 1);
GL.TexCoord2(0, 0);
GL.Vertex2(-1, 1);
GL.End();
}
Shader used:
[Shader vertex]
#version 150 core
in vec2 _pos;
out vec2 texCoord;
uniform float _time;
uniform sampler2D tex;
void main() {
gl_Position = vec4(_pos, 0, 1);
texCoord = _pos/2+vec2(0.5,0.5);
texCoord.y = 1 - texCoord.y;
}
[Shader fragment]
#version 150 core
#define PI 3.1415926535897932384626433832795
out vec4 outColor;
uniform float _time;
uniform sampler2D tex;
in vec2 texCoord;
//
void main() {
outColor = texture2D(tex, texCoord);
}
Somehow the rendered scene gets turned upside down by this. Why ?

Answer 1

I think I found my mistake. I had the texture coordinates AND the camera inverted. It seems to be fixed now. Why I still don't undestand is, why this works:
[Shader vertex]
#version 150 core
in vec2 _pos;
out vec2 texCoord;
uniform float _time;
uniform sampler2D tex;
void main() {
gl_Position = vec4(_pos, 0, 1);
texCoord = _pos/2+vec2(0.5,0.5);
//texCoord.y = 1 - texCoord.y;
}
[Shader fragment]
#version 150 core
#define PI 3.1415926535897932384626433832795
out vec4 outColor;
uniform float _time;
uniform sampler2D tex;
in vec2 texCoord;
//
void main() {
outColor = texture2D(tex, texCoord);
}
I would've expected that the y coordinate of the tex coord would need to be inverted.