Glass panes not correctly rendering with the back of stairs

Exactly like fuj1n explains. And that is the part I'm going to "attack". I'll add similar smartness as in the torch placement bug. Just it wasn't as trivial to apply to this issue as to the other one, due to some design decisions/architecture hiccups. I'm still at work, but I'll get to this later today.

Sample screenshot 'fixed-panes-stairs.png' showing both torches attached and glass panes connected to backside of stair blocks. Code fixes incoming.

(NOTE: would be best to fix all of this, MC-8345 and MC-2938 at the same time; see the MC-2938 for more text.)

Fix
The basic reason for the issue is the same as for the MC-8345; the code does not have own method to check only surfaces of blocks, so it checks just the full block type, and also typically has some special case handling here and there (like fuj1n explained for this issue).

To resolve the torches vs. backs of stairs, I added a method to check just for the block's surface (if it is a full and solid surface). It didn't directly work for this issue, as it was made just for the torch-stuff at the time. I made the necessary changes to accommodate both issues, and as a side-effect, made the new method work more correctly. (I'll update the code in the other issue, too.)

However, I also had to adjust certain method calls in a way that may have some undesired side-effects. Testing recommended.

Here are the code changes, using mix of MCP and my own namings:

Block

/**
     * Override as necessary.
     * @param side 1 = bottom, 2 = z+1, 3 = z-1, 4 = x+1, 5 = x-1,  top = 0 or anything else
     * @return true if that side is solid and full surface
     */
    public boolean hasSolidFullSurfaceAt(IBlockAccess access, int x, int y, int z, int side) {
        switch (side) {
            case 1: return access.isBlockNormalCube(x, y, z);
            case 2:
            case 3:
            case 4:
            case 5: return access.isBlockNormalCube(x, y, z);
            default: return access.doesBlockHaveSolidTopSurface(x, y, z);
        }
    }

BlockStairs

public boolean hasSolidFullSurfaceAt(IBlockAccess access, int x, int y, int z, int side) {
        int metaData = access.getBlockMetadata(x, y, z);
        switch (side) {
            case 1: return (metaData & 4) == 0;
            case 2: return (metaData & 3) == 3;
            case 3: return (metaData & 3) == 2;
            case 4: return (metaData & 3) == 1;
            case 5: return (metaData & 3) == 0;
            default: return (metaData & 4) == 1; // true if it is upside down
        }
    }

BlockPane

public void addCollidingBlockToList(World world, int x, int y, int z, AxisAlignedBB par5AxisAlignedBB, List par6List, Entity par7Entity) {
//        boolean north = this.canThisPaneConnectToThisBlockID(world.getBlockId(x, y, z - 1));
//        boolean south = this.canThisPaneConnectToThisBlockID(world.getBlockId(x, y, z + 1));
//        boolean west = this.canThisPaneConnectToThisBlockID(world.getBlockId(x - 1, y, z));
//        boolean east = this.canThisPaneConnectToThisBlockID(world.getBlockId(x + 1, y, z));
        boolean north = this.canPaneAtConnectToDir(world, x, y, z, 3);
        boolean south = this.canPaneAtConnectToDir(world, x, y, z, 2);
        boolean west = this.canPaneAtConnectToDir(world, x, y, z, 5);
        boolean east = this.canPaneAtConnectToDir(world, x, y, z, 4);
        ...

    public void setBlockBoundsBasedOnState(IBlockAccess blockAccess, int x, int y, int z) {
        ...
//        boolean north = this.canThisPaneConnectToThisBlockID(blockAccess.getBlockId(x, y, z - 1));
//        boolean south = this.canThisPaneConnectToThisBlockID(blockAccess.getBlockId(x, y, z + 1));
//        boolean west = this.canThisPaneConnectToThisBlockID(blockAccess.getBlockId(x - 1, y, z));
//        boolean east = this.canThisPaneConnectToThisBlockID(blockAccess.getBlockId(x + 1, y, z));
        boolean north = this.canPaneAtConnectToDir(blockAccess, x, y, z, 3);
        boolean south = this.canPaneAtConnectToDir(blockAccess, x, y, z, 2);
        boolean west = this.canPaneAtConnectToDir(blockAccess, x, y, z, 5);
        boolean east = this.canPaneAtConnectToDir(blockAccess, x, y, z, 4);
        ...

    /**
     * ADDED METHOD.
     * @param dir 1 = bottom, 2 = z+1, 3 = z-1, 4 = x+1, 5 = x-1,  top = 0 or anything else
     */
    public final boolean canPaneAtConnectToDir(IBlockAccess access, int x, int y, int z, int dir) {
        switch (dir) {
            case 2: { z++; break; }
            case 3: { z--; break; }
            case 4: { x++; break; }
            case 5: { x--; break; }
            default: return false;
        }
        
        int blockId = access.getBlockId(x, y, z);
        if (this.canThisPaneConnectToThisBlockID(blockId)) return true; // Old check
        // ADDED CHECK (compared to old operation), THE CORE OF THIS FIX:
        Block block = Block.blocksList[blockId];
        if (block == null)
            return false;
        return block.hasSolidFullSurfaceAt(access, x, y, z, dir);
    }

RenderBlocks.renderBlockPane()

...
//        boolean north = par1BlockPane.canThisPaneConnectToThisBlockID(this.blockAccess.getBlockId(x, y, z - 1));
//        boolean south = par1BlockPane.canThisPaneConnectToThisBlockID(this.blockAccess.getBlockId(x, y, z + 1));
//        boolean west = par1BlockPane.canThisPaneConnectToThisBlockID(this.blockAccess.getBlockId(x - 1, y, z));
//        boolean east = par1BlockPane.canThisPaneConnectToThisBlockID(this.blockAccess.getBlockId(x + 1, y, z));
        boolean north = blockPane.canPaneAtConnectToDir(blockAccess, x, y, z, 3);
        boolean south = blockPane.canPaneAtConnectToDir(blockAccess, x, y, z, 2);
        boolean west = blockPane.canPaneAtConnectToDir(blockAccess, x, y, z, 5);
        boolean east = blockPane.canPaneAtConnectToDir(blockAccess, x, y, z, 4);
        ...

I tested changes on 1.4.7, results as in the screenshot. (Though the torches need also the MC-8345 fixes applied, too.)

Affects 13w09b.

Affects 13w09c.

Markku wrote a fix... why is this still unresolved?

I seriously hope this is not considered to be intended behavior. Voted.

I am seeing the same issue in the new 1.7.2 release.

Confirmed for 1.7.5, 14w08a and 14w10c

Confirmed for 14w11b

Confirmed in 1.8.1-pre1.

Confirmed in 1.8.1-pre5.

Still happening in 15w42a.

Still happening in 15w44b.

Still happening in 15w45a.